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Some text was adapted from the 3rd edition Encyclopaedia article “Aviation - ground personnel” authored by E. Evrard.
Commercial air transport involves the interaction of several groups including governments, airport operators, aircraft operators and aircraft manufacturers. Governments are generally involved in overall air transport regulation, oversight of aircraft operators (including maintenance and operations), manufacturing certification and oversight, air traffic control, airport facilities and security. Airport operators can either be local governments or commercial entities. They are usually responsible for the general operation of the airport. Types of aircraft operators include general airlines and commercial transport (either privately or publicly owned), cargo carriers, corporations and individual aircraft owners. Aircraft operators in general are responsible for operation and maintenance of the aircraft, training of personnel and operation of ticketing and boarding operations. Responsibility for security can vary; in some countries the aircraft operators are responsible, and in others the government or airport operators are responsible. Manufacturers are responsible for design, manufacturing and testing, and for aircraft support and improvement. There are also international agreements con- cerning international flights.
This article deals with the personnel involved with all aspects of flight control (i.e., those who control commercial aircraft from takeoff to landing and who maintain the radar towers and other facilities used for flight control) and with those airport personnel who perform maintenance on and load aircraft, handle baggage and air freight and provide passenger services. Such personnel are divided into the following categories:
Flight Control Operations
Government aviation authorities such as the Federal Aviation Administration (FAA) in the United States maintain flight control over commercial aircraft from takeoff to landing. Their primary mission involves the handling of airplanes using radar and other surveillance equipment to keep aircraft separated and on course. Flight control personnel work at airports, terminal radar approach control facilities (Tracons) and regional long-distance centres, and consist of air traffic controllers and airways facilities maintenance personnel. Airways facilities maintenance personnel maintain the airport control towers, air traffic Tracons and regional centres, radio beacons, radar towers and radar equipment, and consist of electronics technicians, engineers, electricians and facilities maintenance workers. The guidance of planes using instruments is accomplished following instrument flight rules (IFR). Planes are tracked using the General National Air Space System (GNAS) by air traffic controllers working at airport control towers, Tracons and regional centres. Air traffic controllers keep planes separated and on course. As a plane moves from one jurisdiction to another, responsibility for the plane is handed from one type of controller to another.
Regional centres, terminal radar approach control and airport control towers
Regional centres direct planes after they have reached high altitudes. A centre is the largest of the aviation authority’s facilities. Regional centre controllers hand off and receive planes to and from Tracons or other regional control centres and use radio and radar to maintain communication with aircraft. A plane flying across a country will always be under surveillance by a regional centre and passed along from one regional centre to the next.
The regional centres all overlap each other in the surveillance range and receive radar information from long-range radar facilities. Radar information is sent to these facilities via microwave links and telephone lines, thus providing a redundancy of information so that if one form of communication is lost, the other is available. Oceanic air traffic, which cannot be seen by radar, is handled by the regional centres via radio. Technicians and engineers maintain the electronic surveillance equipment and the uninterrupted power systems, which includes emergency generators and large banks of back-up batteries.
Air traffic controllers at Tracons handle planes flying at low altitudes and within 80 km of airports, using radio and radar to maintain communication with aircraft. Tracons receive radar tracking information from the airport surveillance radar (ASR). The radar tracking system identifies the plane moving in space but also queries the plane beacon and identifies the plane and its flight information. Personnel and work tasks at Tracons are similar to those at the regional centres.
Regional and approach control systems exist in two variants: non-automated or manual systems and automated systems.
With manual air traffic control systems, radio communications between controller and pilot are supplemented by information from primary or secondary radar equipment. The trace of the aeroplane can be followed as a mobile echo on display screens formed by cathode-ray tubes (see figure 1). Manual systems have been replaced by automated systems in most countries.
Figure 1. Air traffic controller at a manual local control centre radar screen.
With automated air traffic control systems, information on the aeroplane is still based on the flight plan and primary and secondary radar, but computers make it possible to present in alphanumeric form on the display screen all data concerning each aeroplane and to follow its route. Computers are also used to anticipate conflict between two or more aircraft on identical or converging routes on the basis of the flight plans and standard separations. Automation relieves the controller of many of the activities he or she carries out in a manual system, leaving more time for taking decisions.
Conditions of work are different in manual and automated control centre systems. In the manual system the screen is horizontal or sloping, and the operator leans forward in an uncomfortable position with his or her face between 30 and 50 cm from it. The perception of mobile echoes in the form of spots depends on their brightness and their contrast with the illuminance of the screen. As some mobile echoes have a very low luminous intensity, the working environment must be very weakly illuminated to ensure the greatest possible visual sensitivity to contrast.
In the automated system the electronic data display screens are vertical or almost vertical, and the operator can work in a normal sitting position with a greater reading distance. The operator has horizontally arranged keyboards within reach to regulate the presentation of the characters and symbols conveying the various types of information and can alter the shape and brightness of the characters. The lighting of the room can approach the intensity of daylight, for contrast remains highly satisfactory at 160 lux. These features of the automated system place the operator in a much better position to increase efficiency and reduce visual and mental fatigue.
Work is carried out in a huge, artificially lighted room without windows, which is filled with display screens. This closed environment, often far from the airports, allows little social contact during the work, which calls for great concentration and powers of decision. The comparative isolation is mental as well as physical, and there is hardly any opportunity of diversion. All this has been held to produce stress.
Each airport has a control tower. Controllers at airport control towers direct planes in and out of the airport, using radar, radio and binoculars to maintain communication with aircraft both while taxiing and while taking off and landing. Airport tower controllers hand off to or receive planes from controllers at Tracons. Most of the radar and other surveillance systems are located at the airports. These systems are maintained by technicians and engineers.
The walls of the tower room are transparent, for there must be perfect visibility. The working environment is thus completely different from that of regional or approach control. The air traffic controllers have a direct view of aircraft movements and other activities. They meet some of the pilots and take part in the life of the airport. The atmosphere is no longer that of a closed environment, and it offers a greater variety of interest.
Airways facilities maintenance personnel
Airways facilities and radar towers maintenance personnel consist of radar technicians, navigational and communication technicians and environmental technicians.
Radar technicians maintain and operate the radar systems, including airport and long-range radar systems. The work involves electronic equipment maintenance, calibration and troubleshooting.
Navigational and communication technicians maintain and operate the radio communications equipment and other related navigational equipment used in controlling air traffic. The work involves electronic equipment maintenance, calibration and troubleshooting.
Environmental technicians maintain and operate the aviation authority buildings (regional centres, Tracons and airport facilities, including the control towers) and equipment. The work requires running heating, ventilation and air-conditioning equipment and maintaining emergency generators, airport lighting systems, large banks of batteries in uninterrupted power supply (UPS) equipment and related electrical power equipment.
The occupational hazards for all three jobs include: noise exposure; working on or near live electrical parts including exposure to high voltage, x-ray exposure from klystron and magnitron tubes, fall hazards while working on elevated radar towers or using climbing poles and ladders to access towers and radio antenna and possibly PCBs exposure when handling older capacitors and working on utility transformers. Workers may also be exposed to microwave and radio-frequency exposure. According to a study of a group of radar workers in Australia (Joyner and Bangay 1986), personnel are not generally exposed to levels of microwave radiation exceeding 10 W/m2 unless they are working on open waveguides (microwave cables) and components utilizing waveguide slots, or working within transmitter cabinets when high-voltage arcing is occurring. The environmental technicians also work with chemicals related to building maintenance, including boiler and other related water treatment chemicals, asbestos, paints, diesel fuel and battery acid. Many of the electrical and utility cables at airports are underground. Inspection and repair work on these systems often involves confined space entry and exposure to confined space hazards—noxious or asphyxiating atmospheres, falls, electrocution and engulfment.
Airways facilities maintenance workers and other ground crews in the airport operating area are frequently exposed to jet exhaust. Several airport studies where sampling of jet engine exhaust has been conducted demonstrated similar results (Eisenhardt and Olmsted 1996; Miyamoto 1986; Decker 1994): the presence of aldehydes including butyraldehyde, acetaldehyde, acrolein, methacrolein, isobutyraldehyde, propionaldehyde, croton-aldehyde and formaldehyde. Formaldehyde was present at significantly higher concentrations then the other aldehydes, followed by acetaldehyde. The authors of these studies have concluded that the formaldehyde in the exhaust was probably the main causative factor in the eye and respiratory irritation reported by exposed persons. Depending on the study, nitrogen oxides either were not detected or were present in concentrations below 1 part per million (ppm) in the exhaust stream. They concluded that neither nitrogen oxides nor other oxides play a major role in the irritation. Jet exhaust was also found to contain 70 different hydrocarbon species with up to 13 consisting mostly of olefins (alkenes). Heavy-metal exposure from jet exhaust has been shown not to pose a health hazard for areas surrounding airports.
Radar towers should be equipped with standard railings around the stairs and platforms to prevent falls and with interlocks to prevent access to the radar dish while it is operating. Workers accessing towers and radio antennas should use approved devices for ladder climbing and personal fall protection.
Personnel work on both de-energized and energized electrical systems and equipment. Protection from electrical hazards should involve training in safe work practices, lockout/tagout procedures and the use of personal protective equipment (PPE).
The radar microwave is generated by high-voltage equipment using a klystron tube. The klystron tube generates x rays and can be a source of exposure when the panel is opened, allowing personnel to come in close proximity to it to work on it. The panel should always remain in place except when servicing the klystron tube, and work time should be kept to a minimum.
Personnel should wear the appropriate hearing protection (e.g., ear plugs and/or ear muffs) when working around noise sources such as jet planes and emergency generators.
Other controls involve training in materials handling, vehicle safety, emergency response equipment and evacuation procedures and confined space entry procedures equipment (including direct-reading air monitors, blowers and mechanical retrieval systems).
Air traffic controllers and flight services personnel
Air traffic controllers work in regional control centres, Tracons and airport control towers. This work generally involves working at a console tracking planes on radar scopes and communicating with pilots by radio. Flight services personnel provide weather information for pilots.
The hazards to air traffic controllers include possible visual problems, noise, stress and ergonomic problems. At one time there was concern about x-ray emissions from the radar screens. This, however, has not turned out to be a problem at the operating voltages used.
Standards of fitness for air traffic controllers have been recommended by the International Civil Aviation Organization (ICAO), and detailed standards are set out in national military and civil regulations, those relating to sight and hearing being particularly precise.
The broad, transparent surfaces of air traffic control towers at airports sometimes result in dazzling by the sun, and reflection from surrounding sand or concrete can increase the luminosity. This strain on the eyes may produce headaches, though often of a temporary nature. It may be prevented by surrounding the control tower with grass and avoiding concrete, asphalt or gravel and by giving a green tint to the transparent walls of the room. If the colour is not too strong, visual acuity and colour perception remain adequate while the excess radiation that causes dazzle is absorbed.
Until about 1960 there was a good deal of disagreement among authors on the frequency of eyestrain among controllers from viewing radar screens, but it does seem to have been high. Since then, attention given to visual refractive errors in the selection of radar controllers, their correction among serving controllers and the constant improvement of working conditions at the screen have helped to lower it considerably. Sometimes, however, eyestrain appears among controllers with excellent sight. This may be attributed to too low a level of lighting in the room, irregular illumination of the screen, the brightness of the echoes themselves and, in particular, flickering of the image. Progress in viewing conditions and insistence on higher technical specifications for new equipment are leading to a marked reduction in this source of eyestrain, or even its elimination. Strain in accommodation has also been considered until recently to be a possible cause of eyestrain among operators who have worked very close to the screen for an hour without interruption. Visual problems are becoming much less frequent and are likely to disappear or to occur only very occasionally in the automated radar system, for example, when there is a fault in a scope or where the rhythm of the images is badly adjusted.
A rational arrangement of the premises is mainly one that facilitates the adaptation of the scope readers to the intensity of the ambient lighting. In a non-automated radar station, adaptation to the semi-darkness of the scope room is achieved by spending 15 to 20 minutes in another dimly lighted room. The general lighting of the scope room, the luminous intensity of the scopes and the brightness of the spots must all be studied with care. In the automated system the signs and symbols are read under an ambient lighting of from 160 to 200 lux, and the disadvantages of the dark environment of the non-automated system are avoided. With regard to noise, despite modern sound-insulating techniques, the problem remains acute in control towers installed near the runways.
Readers of radar screens and electronic display screens are sensitive to changes in the ambient lighting. In the non-automated system the controllers must wear glasses absorbing 80% of the light for between 20 and 30 minutes before entering their workplace. In the automated system special glasses for adaptation are no longer essential, but persons particularly sensitive to the contrast between the lighting of the symbols on the display screen and that of the working environment find that glasses of medium absorptive power add to the comfort of their eyes. There is also a reduction in eyestrain. Runway controllers are well advised to wear glasses absorbing 80% of the light when they are exposed to strong sunlight.
The most serious occupational hazard for air traffic controllers is stress. The chief duty of the controller is to make decisions on the movements of aircraft in the sector he or she is responsible for: flight levels, routes, changes of course when there is conflict with the course of another aircraft or when congestion in one sector leads to delays, air traffic and so on. In non-automated systems the controller must also prepare, classify and organize the information his or her decision is based on. The data available are comparatively crude and must first be digested. In highly automated systems the instruments can help the controller in taking decisions, and he or she may then only have to analyse data produced by teamwork and presented in rational form by these instruments. Although the work may be greatly facilitated, the responsibility for approving the decision proposed to the controller remains the controller’s, and his or her activities still give rise to stress. The responsibilities of the job, pressure of work at certain hours of dense or complex traffic, increasingly crowded air space, sustained concentration, rotating shift work and awareness of the catastrophe that may result from an error all create a situation of continuous tension, which may lead to stress reactions. The fatigue of the controller may assume the three classic forms of acute fatigue, chronic fatigue or overstrain and nervous exhaustion. (See also the article “Case Studies of Air Traffic Controllers in the United States and Italy”.)
Air traffic control calls for an uninterrupted service 24 hours a day, all year long. The conditions of work of controllers thus include shift work, an irregular rhythm of work and rest and periods of work when most other people are enjoying holidays. Periods of concentration and of relaxation during working hours and days of rest during a week of work are indispensable to the avoidance of operational fatigue. Unfortunately, this principle cannot be embodied in general rules, for the arrangement of work in shifts is influenced by variables that may be legal (maximum number of consecutive hours of work authorized) or purely professional (workload depending on the hour of the day or the night), and by many other factors based on social or family considerations. With regard to the most suitable length for periods of sustained concentration during work, experiments show that there should be short breaks of at least a few minutes after periods of uninterrupted work of from half an hour to an hour-and-a-half, but that there is no need to be bound by rigid patterns to achieve the desired aim: the maintenance of the level of concentration and the prevention of operational fatigue. What is essential is to be able to interrupt the periods of work at the screen with periods of rest without interrupting the continuity of the shift work. Further study is necessary to establish the most suitable length of the periods of sustained concentration and of relaxation during work and the best rhythm for weekly and annual rest periods and holidays, with a view to drawing up more unified standards.
There are also ergonomic issues while working at the consoles similar to those of computer operators, and there may be indoor air quality problems. Air traffic controllers also experience tone incidents. Tone incidents are loud tones coming into the headsets. The tones are of short duration (a few seconds) and have sound levels up to 115 dBA.
In flight services work, there are hazards associated with lasers, which are used in ceilorometer equipment used to measure cloud ceiling height, as well as ergonomic and indoor air quality issues.
Other flight control services personnel
Other flight control services personnel include flight standards, security, airport facilities renovation and construction, administrative support and medical personnel.
Flight standards personnel are aviation inspectors who conduct airline maintenance and flight inspections. Flight standards personnel verify the airworthiness of the commercial airlines. They often inspect airplane maintenance hangers and other airport facilities, and they ride in the cockpits of commercial flights. They also investigate plane crashes, incidents or other aviation-related mishaps.
The hazards of the job include noise exposure from aircraft, jet fuel and jet exhaust while working in hangers and other airport areas, and potential exposure to hazardous materials and blood-borne pathogens while investigating aircraft crashes. Flight standards personnel face many of the same hazards as airport ground crews, and thus many of the same precautions apply.
Security personnel include sky marshals. Sky marshals provide internal security on airplanes and external security at airport ramps. They are essentially police and investigate criminal activities related to aircraft and airports.
Airport facilities renovation and construction personnel approve all plans for airport modifications or new construction. The personnel are usually engineers, and their work largely involves office work.
Administrative workers include personnel in accounting, management systems and logistics. Medical personnel in the flight surgeon’s office provide occupational medical services to aviation authority workers.
Air traffic controllers, flight services personnel and personnel who work in office environments should have ergonomic training on proper sitting postures and on emergency response equipment and evacuation procedures.
Airport ground crews conduct maintenance on and load aircraft. Baggage handlers handle passenger baggage and air freight, whereas passenger service agents register passengers and check passenger baggage.
All loading operations (passengers, baggage, freight, fuel, supplies and so on) are controlled and integrated by a supervisor who prepares the loading plan. This plan is given to the pilot prior to take-off. When all operations have been completed and any checks or inspections considered necessary by the pilot have been made, the airport controller gives authorization for take-off.
Aircraft maintenance and servicing
Every aircraft is serviced every time it lands. Ground crews performing routine turnaround maintenance; conduct visual inspections, including checking the oils; perform equipment checks, minor repairs and internal and external cleaning; and refuel and restock the aircraft. As soon as the aircraft lands and arrives in the unloading bays, a team of mechanics begins a series of maintenance checks and operations which vary with the type of aircraft. These mechanics refuel the aircraft, check a number of safety systems which must be inspected after each landing, investigate the logbook for any reports or defects the flight crew may have noticed during the flight and, where necessary, make repairs. (See also the article “Aircraft Maintenance Operations” in this chapter.) In cold weather, the mechanics may have to perform additional tasks, such as de-icing of wings, landing gear, flaps and so on. In hot climates special attention is paid to the condition of the aircraft’s tyres. Once this work has been completed, the mechanics can declare the aircraft flightworthy.
More thorough maintenance inspections and aircraft overhauls are performed at specific intervals of flying hours for each aircraft.
Fuelling aircraft is one of the most potentially hazardous servicing operations. The amount of fuel to be loaded is determined on the basis of such factors as flight duration, take-off weight, flight path, weather and possible diversions.
A cleaning team cleans and services the aircraft cabins, replacing dirty or damaged material (cushions, blankets and so on), empties the toilets and refills the water tanks. This team may also disinfect or disinfest the aircraft under the supervision of public health authorities.
Another team stocks the aircraft with food and drink, emergency equipment and supplies needed for passenger comfort. Meals are prepared under high standards of hygiene to eliminate the risk of food poisoning, particularly among the flight crew. Certain meals are deep frozen to –40ºC, stored at –29ºC and reheated in flight.
Ground service work includes the use of motorized and non-motorized equipment.
Baggage and air cargo loading
Baggage and cargo handlers move passenger baggage and air freight. Freight can range from fresh fruits and vegetables and live animals to radioisotopes and machinery. Because baggage and cargo handling requires physical effort and the use of mechanized equipment, workers may be more at risk for injuries and ergonomic problems.
Ground crews and baggage and freight handlers are exposed to many of the same hazards. These hazards include working outdoors in all types of weather, exposure to potential airborne contaminants from jet fuel and jet engine exhaust and exposure to prop wash and jet blast. Prop wash and jet blast can slam doors shut, knock people or unsecured equipment over, cause turboprop propellers to rotate and blow debris into engines or onto people. Ground crews are also exposed to noise hazards. A study in China showed ground crews were exposed to noise at aircraft engine hatches that exceeds 115 dBA (Wu et al. 1989). Vehicle traffic on the airport ramps and apron is very heavy, and the risk of accidents and collision is high. Fuelling operations are very hazardous, and workers may be exposed to fuel spills, leaks, fires and explosions. Workers on lifting devices, aerial baskets, platforms or access stands are at risk of falling. Job hazards also include rotating shift work carried out under pressure of time.
Strict regulations must be implemented and enforced for vehicle movement and driver training. Driver training should emphasize complying with speed limits, obeying off-limit areas and ensuring that there is adequate room for planes to manoeuvre. There should be good maintenance of ramp surfaces and efficient control of ground traffic. All vehicles authorized to operate on the airfield should be conspicuously marked so they can be readily identified by air traffic controllers. All equipment used by the ground crews should be regularly inspected and maintained. Workers on lifting devices, aerial baskets, platforms or access stands must be protected from falls either through the use of guardrails or personal fall protection equipment. Hearing protection equipment (earplugs and earmuffs) must be used for protection against noise hazards. Other PPE includes suitable work clothing depending on the weather, non-slip reinforced-toe-cap foot protection and appropriate eye, face, glove and body protection when applying de-icing fluids. Rigorous fire prevention and protection measures including bonding and grounding and prevention of electric sparking, smoking, open flames and the presence of other vehicles within 15 m of aircraft, must be implemented for refuelling operations. Fire-fighting equipment should be maintained and located in the area. Training on procedures to follow in the event of a fuel spill or fire should be conducted regularly.
Baggage and freight handlers should store and stack cargo securely and should receive training on proper lifting techniques and back postures. Extreme care should be used when entering and leaving aircraft cargo areas from carts and tractors. Appropriate protective clothing should be worn, depending on the type of cargo or baggage (such as gloves when handling live animal cargo). Baggage and freight conveyors, carousels and dispensers should have emergency shut-offs and built-in guards.
Passenger service agents
Passenger service agents issue tickets, register and check in passengers and passenger baggage. These agents may also guide passengers when boarding. Passenger service agents who sell airline tickets and check in passengers may spend all day on their feet using a video display unit (VDU). Precautions against these ergonomic hazards include resilient floor mats and seats for relief from standing, work breaks and ergonomic and anti-glare measures for the VDUs. In addition, dealing with passengers can be a source of stress, particularly when there are delays in flights or problems with making flight connections and so on. Breakdowns in the computerized airline reservations systems can also be a major source of stress.
Baggage check-in and weigh-in facilities should minimize the need for employees and passengers to lift and handle bags, and baggage conveyors, carousels and dispensers should have emergency shut-offs and built-in guards. Agents should also receive training on proper lifting techniques and back postures.
Baggage inspection systems use fluoroscopic equipment to examine baggage and other carry-on items. Shielding protects workers and the public from x-ray emissions, and if the shielding is not properly positioned, interlocks prevent the system from operating. According to an early study by the US National Institute for Occupational Safety and Health (NIOSH) and the Air Transport Association at five US airports, maximum documented whole-body x-ray exposures were considerably lower than maximum levels set by the US Food and Drug Administration (FDA) and the Occupational Safety and Health Administration (OSHA) (NIOSH 1976). Workers should wear whole-body monitoring devices to measure radiation exposures. NIOSH recommended periodic maintenance programmes to check effectiveness of shielding.
Passenger service agents and other airport personnel must be thoroughly familiar with the airport emergency evacuation plan and procedures.
High levels of stress among air traffic controllers (ATCs) were first widely reported in the United States in the 1970 Corson Report (US Senate 1970), which focused on working conditions such as overtime, few regular work breaks, increasing air traffic, few vacations, poor physical work environment and “mutual resentment and antagonism” between management and labour. Such conditions contributed to ATC job actions in 1968–69. In addition, early medical research, including a major 1975–78 Boston University study (Rose, Jenkins and Hurst 1978), suggested that ATCs may face a higher risk of stress-related illness, including hypertension.
Following the 1981 US ATC strike, in which job stress was a major issue, the Department of Transportation again appointed a task force to examine stress and morale. The resulting 1982 Jones Report indicated that FAA employees in a wide variety of job titles reported negative results for job design, work organization, communication systems, supervisory leadership, social support and satisfaction. The typical form of ATC stress was an acute episodic incident (such as a near mid-air collision) along with interpersonal tensions stemming from management style. The task force reported that 6% of the ATC sample was “burned out” (having a large and debilitating loss of self-confidence in ability to do the job). This group represented 21% of those 41 years of age and older and 69% of those with 19 or more years of service.
A 1984 review by the Jones task force of its recommendations concluded that “conditions are as bad as in 1981, or perhaps a bit worse”. Major concerns were increasing traffic volume, inadequate staffing, low morale and an increasing burnout rate. Such conditions led to the re-unionization of US ATCs in 1987 with the election of the National Air Traffic Controllers Organization (NATCA) as their bargaining representative.
In a 1994 survey, New York City area ATCs reported continuing staffing shortages and concerns about job stress, shift work and indoor air quality. Recommendations for improving morale and health included transfer opportunities, early retirement, more flexible schedules, exercise facilities at work and increased staffing. In 1994, a greater proportion of Level 3 and 5 ATCs reported high burnout than ATCs in 1981 and 1984 national surveys (except for ATCs working in centres in 1984). Level 5 facilities have the highest level of air traffic, and Level 1, the lowest (Landsbergis et al. 1994). Feelings of burnout were related to having experienced a “near miss” in the past 3 years, age, years working as an ATC, working in high-traffic Level 5 facilities, poor work organization and poor supervisor and co-worker support.
Research also continues on appropriate shift schedules for ATCs, including the possibility of a 10-hour, 4-day shift schedule. The long-term health effects of the combination of rotating shifts and compressed work weeks are not known.
A collectively bargained programme to reduce ATC job stress in Italy
The company in charge of all civil air traffic in Italy (AAAV) employs 1,536 ATCs. AAAV and union representatives drew up several agreements between 1982 and 1991 to improve working conditions. These include:
1. Modernizing radio systems and automating aeronautical information, flight data processing and air traffic management. This provided for more reliable information and more time for making decisions, eliminating many risky traffic peaks and providing for a more balanced workload.
2. Reducing work hours. The operative work week is now 28 to 30 hours.
3. Changing shift schedules:
4. Reduce environmental stressors. Attempts have been made to reduce noise and provide more light.
5. Improving the ergonomics of new consoles, screens and chairs.
6. Improving physical fitness. Gyms are provided in the largest facilities.
Research during this period suggests that the programme was beneficial. The night shift was not very stressful; ATCs’ performance did not worsen significantly at the end of three shifts; only 28 ATCs were dismissed for health reasons in 7 years; and a large decline in “near misses” occurred despite major increases in air traffic.
Aircraft maintenance operations are broadly distributed within and across nations and are performed by both military and civilian mechanics. Mechanics work at airports, maintenance bases, private fields, military installations and aboard aircraft carriers. Mechanics are employed by passenger and freight carriers, by maintenance contractors, by operators of private fields, by agricultural operations and by public and private fleet owners. Small airports may provide employment for a few mechanics, while major hub airports and maintenance bases may employ thousands. Maintenance work is divided between that which is necessary to maintain ongoing daily operations (line maintenance) and those procedures that periodically check, maintain and refurbish the aircraft (base maintenance). Line maintenance comprises en route (between landing and takeoff) and overnight maintenance. En route maintenance consists of operational checks and flight-essential repairs to address discrepancies noted during flight. These repairs are typically minor, such as replacing warning lights, tyres and avionic components, but may be as extensive as replacing an engine. Overnight maintenance is more extensive and includes making any repairs deferred during the day’s flights.
The timing, distribution and nature of aircraft maintenance is controlled by each airline company and is documented in its maintenance manual, which in most jurisdictions must be submitted for approval to the appropriate aviation authority. Maintenance is performed during regular checks, designated as A through D checks, specified by the maintenance manual. These scheduled maintenance activities ensure that the entire aircraft has been inspected, maintained and refurbished at appropriate intervals. Lower level maintenance checks may be incorporated into line maintenance work, but more extensive work is performed at a maintenance base. Aircraft damage and component failures are repaired as required.
Line Maintenance Operations and Hazards
En route maintenance is typically performed under a great time constraint at active and crowded flight lines. Mechanics are exposed to prevailing conditions of noise, weather and vehicular and aircraft traffic, each of which may amplify the hazards intrinsic to maintenance work. Climatic conditions may include extremes of cold and heat, high winds, rain, snow and ice. Lightning is a significant hazard in some areas.
Although the current generation of commercial aircraft engines are significantly quieter than previous models, they can still produce sound levels well above those set by regulatory authorities, particularly if the aircraft are required to use engine power in order to exit gate positions. Older jet and turboprop engines can produce sound level exposures in excess of 115 dBA. Aircraft auxiliary-power units (APUs), ground-based power and air-conditioning equipment, tugs, fuel trucks and cargo-handling equipment add to the background noise. Noise levels in the ramp or aircraft parking area are seldom below 80 dBA, thus necessitating the careful selection and routine use of hearing protectors. Protectors must be selected that provide excellent noise attenuation while being reasonably comfortable and permitting essential communication. Dual systems (ear plugs plus ear muffs) provide enhanced protection and allow accom-modation for higher and lower noise levels.
Mobile equipment, in addition to aircraft, may include baggage carts, personnel buses, catering vehicles, ground support equipment and jetways. To maintain departure schedules and customer satisfaction, this equipment must move quickly within often congested ramp areas, even under adverse ambient conditions. Aircraft engines pose the danger of ramp personel being ingested into jet engines or being struck by a propeller or exhaust blasts. Reduced visibility during night and inclement weather increase the risk that mechanics and other ramp personnel might be struck by mobile equipment. Reflective materials on work clothing help to improve visibility, but it is essential that all ramp personnel be well trained in ramp traffic rules, which must be rigorously enforced. Falls, the most frequent cause of serious injuries among mechanics, are discussed elsewhere in this Encyclopaedia.
Chemical exposures in the ramp area include de-icing fluids (usually containing ethylene or propylene glycol), oils and lubricants. Kerosene is the standard commercial jet fuel (Jet A). Hydraulic fluids containing tributyl phosphate cause severe but transient eye irritation. Fuel tank entry, while relatively rare on the ramp, must be included in a comprehensive confined- space-entry programme. Exposure to resin systems used for patching composite areas such as cargo hold panelling may also occur.
Overnight maintenance is typically performed under more controlled circumstances, either in line-service hangers or on inactive flight lines. Lighting, work stands and traction are far better than on the flight line but are likely to be inferior to those found in maintenance bases. Several mechanics may be working on an aircraft simultaneously, necessitating careful planning and coordination to control personnel movement, aircraft component activation (drives, flight control surfaces and so on) and chemical usage. Good housekeeping is essential to prevent clutter from air lines, parts and tools, and to clean spills and drips. These requirements are of even greater importance during base maintenance.
Base Maintenance Operations and Hazards
Maintenance hangars are very large structures capable of accommodating numerous aircraft. The largest hangars can simultaneously accommodate several wide-body aircraft, such as the Boeing 747. Separate work areas, or bays, are assigned to each aircraft undergoing maintenance. Specialized shops for the repair and refitting of components are associated with the hangars. Shop areas typically include sheet metal, interiors, hydraulics, plastics, wheels and brakes, electrical and avionics and emergency equipment. Separate welding areas, paint shops and non-destructive testing areas may be established. Parts-cleaning operations are likely to be found throughout the facility.
Paint hangars with high ventilation rates for workplace air contaminant controls and environmental pollution protection should be available if painting or paint stripping is to be performed. Paint strippers often contain methylene chloride and corrosives, including hydrofluoric acid. Aircraft primers typically contain a chromate component for corrosion protection. Top coats may be epoxy or polyurethane based. Toluene diisocyanate (TDI) is now seldom used in these paints, having been replaced with higher molecular weight isocyanates such as 4,4-diphenylmethane diisocyanate (MDI) or by prepolymers. These still present a risk of asthma if inhaled.
Engine maintenance may be performed within the maintenance base, at a specialized engine overhaul facility or by a sub-contractor. Engine overhaul requires the use of metalworking techniques including grinding, blasting, chemical cleaning, plating and plasma spray. Silica has in most cases been replaced with less hazardous materials in parts cleaners, but the base materials or coatings may create toxic dusts when blasted or ground. Numerous materials of worker health and environmental concern are used in metal cleaning and plating. These include corrosives, organic solvents and heavy metals. Cyanide is generally of the greatest immediate concern, requiring special emphasis in emergency preparedness planning. Plasma spray operations also merit particular attention. Finely divided metals are fed into a plasma stream generated using high-voltage electrical sources and plated onto parts with the concomitant generation of very high noise levels and light energies. Physical hazards include work at height, lifting and work in uncomfortable positions. Precautions include local exhaust ventilation, PPE, fall protection, training in proper lifting and use of mechanized lifting equipment when possible and ergonomic redesign. For example, repetitive motions involved in tasks such as wire tying may be reduced by use of specialized tools.
Military and Agricultural Applications
Military aircraft operations may present unique hazards. JP4, a more volatile jet fuel that Jet A, may be contaminated with n-hexane. Aviation gasoline, used in some propeller-driven aircraft, is highly flammable. Military aircraft engines, including those on transport aircraft, may use less noise abatement than those on commercial aircraft and may be augmented by afterburners. Aboard aircraft carriers the many hazards are significantly increased. Engine noise is augmented by steam catapults and afterburners, flight deck space is extremely limited, and the deck itself is in motion. Because of combat demands, asbestos insulation is present in some cockpits and around hot areas.
The need for lowered radar visibility (stealth) has resulted in the increased use of composite materials on fuselage, wings and flight control structures. These areas may be damaged in combat or from exposure to extremes of climate, requiring extensive repair. Repairs performed under field conditions may result in heavy exposures to resins and composite dusts. Beryllium is also common in military applications. Hydrazide may be present as part of auxiliary-power units, and anti-tank armament may include radioactive depleted uranium rounds. Precautions include appropriate PPE, including respiratory protection. Where possible, portable exhaust systems should be used.
Maintenance work on agricultural aircraft (crop dusters) may result in exposures to pesticides either as a single product or, more likely, as a mixture of products contaminating a single or multiple aircraft. Degradation products of some pesticides are more hazardous than the parent product. Dermal routes of exposure may be significant and may be enhanced by perspiration. Agricultural aircraft and external parts should be thoroughly cleaned before repair, and/or PPE, including skin and respiratory protection, should be used.
Adapted from the 3rd edition Encyclopaedia article “Aviation - flying personnel” authored by H. Gartmann.
This article deals with the occupational safety and health of the crew members of civil aviation aircraft; see also the articles “Airport and flight control operations”, “Aircraft maintenance operations” and “Helicopters” for additional information.
Technical Crew Members
The technical personnel, or flight crew members, are responsible for the operation of the aircraft. Depending on aircraft type, the technical crew includes the pilot-in-command (PIC), the co-pilot (or first officer), and the flight engineer or a second officer (a pilot).
The PIC (or captain) has the responsibility for the safety of the aircraft, the passengers and the other crew members. The captain is the legal representative of the air carrier and is vested by the air carrier and the national aviation authority with the authority to carry out all actions necessary to fulfil this mandate. The PIC directs all duties on the flight deck and is in command of the entire aircraft.
The co-pilot takes his or her orders directly from the PIC and acts as the captain’s deputy upon delegation or in the latter’s absence. The co-pilot is the primary assistant to the PIC in a flight crew; in newer generation, two-person flight deck operations and in older two-engine aircraft, he or she is the only assistant.
Many older generation aircraft carry a third technical crew member. This person may be a flight engineer or a third pilot (usually called the second officer). The flight engineer, when present, is responsible for the mechanical condition of the aircraft and its equipment. New generation aircraft have automated many of the functions of the flight engineer; in these two-person operations, the pilots perform such duties as a flight engineer might otherwise perform that have not been automated by design.
On certain long-distance flights, the crew may be supplemented by a pilot with the qualifications of the PIC, an additional first officer and, when required, an additional flight engineer.
National and international laws stipulate that aircraft technical personnel may operate aircraft only when in possession of a valid licence issued by the national authority. In order to maintain their licences, technical crew members are given ground school training once every year; they are also tested in a flight simulator (a device that simulates real flight and flight emergency conditions) twice a year and in actual operations at least once a year.
Another condition for the receipt and renewal of a valid licence is a medical examination every 6 months for airline transport and commercial pilots over 40 years old, or every 12 months for commercial pilots under 40 years old and for flight engineers. The minimum requirements for these examinations are specified by the ICAO and by national regulations. A certain number of physicians experienced in aviation medicine may be authorized to provide such examinations by the national authorities concerned. These may include air ministry physicians, airforce flight surgeons, airline medical officers or private practitioners designated by the national authority.
Cabin Crew Members
The cabin crew (or flight attendants) are primarily responsible for passenger safety. Flight attendants perform routine safety duties; in addition, they are responsible for monitoring the aircraft cabin for security and safety hazards. In the event of an emergency, the cabin crew members are responsible for the organization of emergency procedures and for the safe evacuation of the passengers. In flight, cabin crew may need to respond to emergencies such as smoke and fire in the cabin, turbulence, medical trauma, aircraft decompressions, and hijackings or other terrorist threats. In addition to their emergency responsibilities, flight attendants also provide passenger service.
The minimum cabin crew ranges from 1 to 14 flight attendants, depending on the type of aircraft, the aircraft’s passenger capacity and national regulations. Additional staffing requirements may be determined by labour agreements. The cabin crew may be supplemented by a purser or service manager. The cabin crew is usually under the supervision of a lead or “in-charge” flight attendant, who, in turn, is responsible and reports directly to the PIC.
National regulations do not usually stipulate that the cabin crew should hold licences in the same way as the technical crew; however, cabin crew are required by all national regulations to have received appropriate instruction and training in emergency procedures. Periodic medical examinations are not usually required by law, but some air carriers require medical examinations for the purposes of health maintenance.
Hazards and Their Prevention
All air crew members are exposed to a wide variety of stress factors, both physical and psychological, to the hazards of an aircraft accident or other flight incident and to the possible contraction of a number of diseases.
Lack of oxygen, one of the main concerns of aviation medicine in the early days of flying, had until recently become a minor consideration in modern air transport. In the case of a jet aircraft flying at 12,000 m altitude, the equivalent altitude in the pressurized cabin is only 2,300 m and, consequently, symptoms of oxygen deficiency or hypoxia will not normally be encountered in healthy persons. Oxygen deficiency tolerance varies from individual to individual, but for a healthy, non-trained subject the presumed altitude threshold at which the first symptoms of hypoxia occur is 3,000 m.
With the advent of new generation aircraft, however, concerns about cabin air quality have resurfaced. Aircraft cabin air consists of air drawn from compressors in the engine and often also contains recirculated air from within the cabin. The flow rate of outside air within an aircraft cabin can vary from as little as 0.2 m3 per minute per person to 1.42 m3 per minute per person, depending upon aircraft type and age, and depending on location within the cabin. New aircraft use recirculated cabin air to a much greater degree than do older models. This air quality issue is specific to the cabin environment. The flight deck compartment air flow rates are often as high as 4.25 m3 per minute per crew member. These higher air flow rates are provided on the flight deck to meet the cooling requirements of the avionic and electronic equipment.
Complaints of poor cabin air quality from cabin crew and passengers have increased in recent years, prompting some national authorities to investigate. Minimal ventilation rates for aircraft cabins are not defined in national regulations. Actual cabin airflow is seldom measured once an aircraft is put into service, since there is no requirement to do so. Minimal air flow and the use of recirculated air, combined with other issues of air quality, such as the presence of chemical contaminants, micro-organisms, other allergens, tobacco smoke and ozone, require further evaluation and study.
Maintaining a comfortable air temperature in the cabin does not represent a problem in modern aircraft; however, the humidity of this air cannot be raised to a comfortable level, due to the large temperature difference between the aircraft interior and exterior. Consequently, both crew and passengers are exposed to extremely dry air, especially on long-distance flights. Cabin humidity depends on the cabin ventilation rate, passenger load, temperature and pressure. The relative humidity found on aircraft today varies from about 25% to less than 2%. Some passengers and crew members experience discomfort, such as dryness of the eyes, nose and throat, on flights that exceed 3 or 4 hours. There is no conclusive evidence of extensive or serious adverse health effects of low relative humidity on flight personnel. However, precautions should be taken to avoid dehydration; adequate intake of liquids such as water and juices should be sufficient to prevent discomfort.
Motion sickness (dizziness, malaise and vomiting due to the abnormal movements and altitudes of the aircraft) was a problem for civil aviation crews and passengers for many decades; the problem still exists today in the case of small sports aircraft, military aircraft and aerial acrobatics. In modern jet transport aircraft, it is much less serious and occurs less frequently due to higher aircraft speeds and take-off weights, higher cruising altitudes (which take the aircraft above the turbulence zones) and the use of airborne radar (which enables squalls and storms to be located and circumnavigated). Additionally, the lack of motion sickness also may be attributed to the more spacious, open design of today’s aircraft cabin, which provides a greater feeling of security, stability and comfort.
Other physical and chemical hazards
Aircraft noise, while a significant problem for ground personnel, is less serious for the crew members of a modern jet aircraft than was the case with the piston-engined plane. The efficiency of noise control measures such as insulation in modern aircraft have helped to eliminate this hazard in most flight environments. Additionally, improvements in communications equipment have minimized background noise levels from these sources.
Ozone exposure is a known but poorly monitored hazard for air crew and passengers. Ozone is present in the upper atmosphere as a result of the photochemical conversion of oxygen by solar ultraviolet radiation at altitudes used by commercial jet aircraft. The mean ambient ozone concentration increases with increasing latitude and is most prevalent during spring. It can also vary with weather systems, with the result of high ozone plumes descending down to lower altitudes.
Symptoms of ozone exposure include cough, upper airway irritation, tickle in the throat, chest discomfort, substantial pain or soreness, difficulty or pain in taking a deep breath, shortness of breath, wheezing, headache, fatigue, nasal congestion and eye irritation. Most people can detect ozone at 0.02 ppm, and studies have shown that ozone exposure at 0.5 ppm or more causes significant decrements in pulmonary function. The effects of ozone contamination are felt more readily by persons engaged in moderate to heavy activity than those who are at rest or engaged in light activity. Thus flight attendants (who are physically active in flight) have experienced the effects of ozone earlier and more frequently than technical crew or passengers on the same flight when ozone contamination was present.
In one study conducted in the late 1970s by the aviation authority in the United States (Rogers 1980), several flights (mostly at 9,150 to 12,200 m) were monitored for ozone contamination. Eleven per cent of the flights monitored were found to exceed that authority’s permissible ozone concentration limits. Methods of minimizing ozone exposure include choice of routes and altitudes that avoid areas of high ozone concentration and the use of air treatment equipment (usually a catalytic converter). The catalytic converters, however, are subject to contamination and loss of efficiency. Regulations (when they exist) do not require their periodic removal for efficiency testing, nor do they require monitoring of ozone levels in actual flight operations. Crew members, especially cabin crew, have requested that better monitoring and control of ozone contamination be implemented.
Another serious concern for technical and cabin crew members is cosmic radiation, which includes radiation forms that are transmitted through space from the sun and other sources in the universe. Most cosmic radiation that travels through space is absorbed by the earth’s atmosphere; however, the higher the altitude, the less the protection. The earth’s magnetic field also provides some shielding, which is greatest near the equator and decreases at the higher latitudes. Air crew members are exposed to cosmic radiation levels inflight that are higher than those received on the ground.
The amount of radiation exposure depends on the type and the amount of flying; for example, a crew member who flies many hours at high altitudes and high latitudes (e.g., polar routes) will receive the greatest amount of radiation exposure. The civil aviation authority in the United States (the FAA) has estimated that the long-term average cosmic radiation dose for air crew members ranges from 0.025 to 0.93 millisieverts (mSv) per 100 block hours (Friedberg et al. 1992). Based on FAA estimates, a crew member flying 960 block hours per year (or an average of 80 hours/month) would receive an estimated annual radiation dose of between 0.24 and 8.928 mSv. These levels of exposure are lower than the recommended occupational limit of 20 millisieverts per year (5-year average) established by the International Commission on Radiological Protection (ICRP).
The ICRP, however, recommends that occupational exposure to ionizing radiation should not exceed 2 mSv during pregnancy. In addition, the US National Council on Radiation Protection and Measurements (NCRP) recommends that exposure not exceed 0.5 mSv in any month once a pregnancy is known. If a crew member worked an entire month on flights with the highest exposures, the monthly dose rate could exceed the recommended limit. Such a pattern of flying over 5 or 6 months could result in an exposure which also would exceed the recommended pregnancy limit of 2 mSv.
The health effects of low-level radiation exposure over a period of years include cancer, genetic defects and birth defects to a child exposed in the womb. The FAA estimates that the added risk of fatal cancer resulting from exposure to inflight radiation would range from 1 in 1,500 to 1 in 94, depending on the type of routes and number of hours flown; the level of added risk of a serious genetic defect resulting from one parent’s exposure to cosmic radiation ranges from 1 in 220,000 live births to 1 in 4,600 live births; and the risk of mental retardation and childhood cancer in a child exposed in utero to cosmic radiation would range between 1 in 20,000 to 1 in 680, depending upon the type and amount of flying the mother did while pregnant.
The FAA report concludes that “radiation exposure is not likely to be a factor that would limit flying for a non-pregnant crew member” because even the largest amount of radiation received annually by a crew member working as much as 1,000 block hours a year is less than half the ICRP recommended average annual limit. However, for a pregnant crew member, the situation is different. The FAA calculates that a pregnant crew member working 70 block hours per month would exceed the recommended 5-month limit on about one-third of the flights they studied (Friedberg et al. 1992).
It should be stressed that these exposure and risk estimates are not universally accepted. Estimates are dependent upon assumptions about the types and mix of radioactive particles encountered at altitude and the weight or quality factor used to determine dose estimates for some of these forms of radiation. Some scientists believe that the actual radiation hazard to air crew members may be greater than described above. Additional monitoring of the flight environment with reliable instrumentation is needed to more clearly determine the extent of inflight radiation exposure.
Until more is known about exposure levels, air crew members should keep their exposure to all types of radiation as low as possible. With respect to inflight radiation exposure, minimizing the amount of flight time and maximizing the distance from the source of radiation can have a direct effect on the dose received. Reducing monthly and yearly flight time and/or selecting flights which fly at lower altitudes and latitudes will reduce exposure. An air crew member who has the ability to control his or her flight assignments might choose to fly fewer hours per month, to bid for a mix of domestic and international flights or to request leaves periodically. A pregnant air crew member might choose to take a leave for the duration of the pregnancy. Since the first trimester is the most crucial time to guard against radiation exposure, an air crew member planning a pregnancy also may want to consider a leave especially if she is flying long-distance polar routes on a regular basis and has no control over her flight assignments.
The main ergonomic problem for technical crew is the need to work for many hours in a sitting but unsettled position and in a very limited working area. In this position (restrained by lap and shoulder harness), it is necessary to carry out a variety of tasks such as movements of the arms, legs and head in different directions, consulting instruments at a distance of about 1 m above, below, to the front and to the side, scanning the far distance, reading a map or manual at close distance (30 cm), listening through earphones or talking through a microphone. Seating, instrumentation, lighting, cockpit microclimate and radio communications equipment comfort have been and still remain the object of continuous improvement. Today’s modern flight deck, often referred to as the “glass cockpit”, has created yet another challenge with its use of leading-edge technology and automation; maintaining vigilance and situational awareness under these conditions has created new concerns for both the designers of aircraft and the technical personnel who fly them.
Cabin crew have an entirely different set of ergonomic problems. One main problem is that of standing and moving around during flight. During climb and descent, and in turbulence, the cabin crew is required to walk on an inclined floor; in some aircraft the cabin incline may remain at approximately 3% during cruise as well. Also, many cabin floors are designed in a manner that creates a rebound effect while walking, putting an additional stress on the flight attendants who are constantly moving about during a flight. Another important ergonomic problem for flight attendants has been the use of mobile carts. These carts can weigh up to 100 to 140 kg and must be pushed and pulled up and down the length of the cabin. Additionally, the poor design and maintenance of the braking mechanisms on many of these carts have caused an increase in repetitive-strain injuries (RSIs) among flight attendants. Air carriers and cart manufacturers are now taking a more serious look at this equipment, and new designs have resulted in ergonomic improvements. Additional ergonomic problems result from the need to lift and carry heavy or bulky items in restricted spaces or while maintaining uncomfortable body posture.
The workload for air crew members depends on the task, the ergonomic layout, the hours of work/duty and many other factors. The additional factors affecting the technical crew include:
Certain of these factors may be equally important for the cabin crew. In addition, the latter are subject to the following specific factors:
The measures taken by air carrier managements and government administrations to keep crew workload within reasonable limits include: improvement and extension of air-traffic control; reasonable limits on hours of duty and requirements for minimum rest provisions; execution of preparatory work by dispatchers, maintenance, catering and cleaning personnel; automation of cockpit equipment and tasks; the standardization of service procedures; adequate staffing; and the provision of efficient and easy-to-handle equipment.
Hours of work
One of the most important factors affecting both technical and cabin crew member occupational health and safety (and certainly the most widely discussed and controversial) is the issue of flight fatigue and recovery. This issue covers the broad spectrum of activity encompassing crew scheduling practices—length of duty periods, amount of flight time (daily, monthly and yearly), reserve or standby duty periods and availability of time for rest both while on flight assignment and at domicile. Circadian rhythms, especially sleep intervals and duration, with all their physiological and psychological implications, are especially significant for air crew members. Time shifts due either to night flights or to east/west or west/east travel across a number of time zones create the greatest problems. Newer generation aircraft, which have the capability of remaining aloft for up to 15 to 16 hours at a time, have exacerbated the conflict between airline schedules and human limitations.
National regulations to limit duty and flight periods and to provide minimum rest limitations exist on a nation by nation basis. In some instances, these regulations have not kept pace with technology or science, nor do they necessarily guarantee flight safety. Until recently there has been little attempt to standardize these regulations. Current attempts at harmonization have given rise to concerns among air crew members that those countries with more protective regulations may be required to accept lower and less adequate standards. In addition to national regulations, many air crew members have been able to negotiate more protective hours of service requirements in their labour agreements. While these negotiated agreements are important, most crew members feel that hours of service standards are essential to their health and safety (and to that of the flying public), and thus minimum standards should be adequately regulated by the national authorities.
In recent years, aircraft crew have been confronted with a serious mental stress factor: the likelihood of hijacking, bombs and armed attacks on aircraft. Although security measures in civil aviation worldwide have been considerably increased and upgraded, the sophistication of terrorists has likewise increased. Air piracy, terrorism and other criminal acts remain a real threat to all air crew members. The commitment and cooperation of all national authorities as well as the force of worldwide public opinion are needed to prevent these acts. Additionally, air crew members must continue to receive special training and information on security measures and must be informed on a timely basis of suspected threats of air piracy and terrorism.
Air crew members understand the importance of starting flight duty in a sufficiently good mental and physical state to ensure that the fatigue and stresses occasioned by the flight itself will not affect safety. Fitness for flight duty may occasionally be impaired by psychological and physical stress, and it is the responsibility of the crew member to recognize whether or not he or she is fit for duty. Sometimes, however, these effects may not be readily apparent to the person under duress. For this reason, most airlines and air crew member associations and labour unions have professional standards committees to assist crew members in this area.
Fortunately, catastrophic aircraft accidents are rare events; nonetheless, they do represent a hazard for air crew members. An aircraft accident is practically never a hazard resulting from a single, well-defined cause; in almost every instance, a number of technical and human factors coincide in the causal process.
Defective equipment design or equipment failure, especially as a result of inadequate maintenance, are two mechanical causes of aircraft accidents. One important, although relatively rare, type of human failure is sudden death due, for example, to myocardial infarction; other failures include sudden loss of consciousness (e.g., epileptic fit, cardiac syncope and fainting due to food poisoning or other intoxication). Human failure may also result from the slow deterioration of certain functions such as hearing or vision, although no major aircraft accident has been attributed to such a cause. Preventing accidents from medical causes is one of the most important tasks of aviation medicine. Careful personnel selection, regular medical examinations, surveys of absence due to illness and accidents, continuous medical contact with working conditions and industrial hygiene surveys can considerably decrease the danger of sudden incapacitation or slow deterioration in technical crew. Medical personnel should also routinely monitor flight scheduling practices to prevent fatigue-related incidents and accidents. A well-operated, modern airline of significant size should have its own medical service for these purposes.
Advances in aircraft accident prevention are often made as a result of careful investigation of accidents and incidents. Systematic screening of all, even minor, accidents and incidents by an accident investigation board comprising technical, operational, structural, medical and other experts is essential to determine all causal factors in an accident or incident and to make recommendations for preventing future occurrences.
A number of strict regulations exist in aviation to prevent accidents caused by use of alcohol or other drugs. Crew members should not consume quantities of alcohol in excess of what is compatible with professional requirements, and no alcohol at all should be consumed during and for at least 8 hours prior to flight duty. Illegal drug use is strictly prohibited. Drug use for medicinal purposes is strictly controlled; such drugs are generally not allowed during or immediately preceding flight, although exceptions may be allowed by a recognized flight physician.
The transport of hazardous materials by air is yet another cause of aircraft accident and incidents. A recent survey covering a 2-year period (1992 to 1993) identified over 1,000 aircraft incidents involving hazardous materials on passenger and cargo air carriers in one nation alone. More recently, an accident in the United States which resulted in the deaths of 110 passengers and crew involved the carriage of hazardous cargo. Hazardous materials incidents in air transportation occur for a number of reasons. Shippers and passengers may be unaware of the dangers presented by the materials they bring aboard aircraft in their baggage or offer for transport. Occasionally, unscrupulous persons may choose to illegally ship forbidden hazardous materials. Additional restrictions on the carriage of hazardous materials by air and improved training for air crew members, passengers, shippers and loaders may help to prevent future incidents. Other accident prevention regulations deal with oxygen supply, crew meals and procedures in case of illness.
Specific occupational disease of crew members are not known or documented. However, certain diseases may be more prevalent among crew members than among persons in other occupations. Common colds and upper respiratory system infections are frequent; this may be due in part to the low humidity during flight, irregularities of schedules, exposure to att large number of people in a confined space and so on. A common cold, especially with upper respiratory congestion, that is not significant for an office worker may incapacitate a crew member if it prevents the clearing of pressure on the middle ear during ascent and, particularly, during descent. Additionally, illnesses that require some form of drug therapy may also preclude the crew member from engaging in work for a period of time. Frequent travel to tropical areas may also entail increased exposure to infectious diseases, the most important being malaria and infections of the digestive system.
The close confines of an aircraft for extended periods of time also carry an excess risk of airborne infectious diseases like tuberculosis, if a passenger or crew member has such a disease in its contagious stage.
Since the first sustained flight of a powered aircraft at Kitty Hawk, North Carolina (United States), in 1903, aviation has become a major international activity. It is estimated that from 1960 to 1989, the annual number of air passengers of regularly scheduled flights increased from 20 million to over 900 million (Poitrast and deTreville 1994). Military aircraft have become indispensable weapons systems for the armed forces of many nations. Advances in aviation technology, in particular the design of life support systems, have contributed to the rapid development of space programmes with human crews. Orbital space flights occur relatively frequently, and astronauts and cosmonauts work in space vehicles and space stations for extended periods of time.
In the aerospace environment, physical stressors that may affect the health of aircrew, passengers and astronauts to some degree include reduced concentrations of oxygen in the air, decreased barometric pressure, thermal stress, acceleration, weightlessness and a variety of other potential hazards (DeHart 1992). This article describes aeromedical implications of exposure to gravity and acceleration during flight in the atmosphere and the effects of microgravity experienced in space.
Gravity and Acceleration
The combination of gravity and acceleration encountered during flight in the atmosphere produces a variety of physiological effects experienced by aircrew and passengers. At the surface of the earth, the forces of gravity affect virtually all forms of human physical activity. The weight of a person corresponds to the force exerted upon the mass of the human body by the earth’s gravitational field. The symbol used to express the magnitude of the acceleration of an object in free fall when it is dropped near the earth’s surface is referred to as g, which corresponds to an acceleration of approximately 9.8 m/s2 (Glaister 1988a; Leverett and Whinnery 1985).
Acceleration occurs whenever an object in motion increases its velocity. Velocity describes the rate of movement (speed) and direction of motion of an object. Deceleration refers to acceleration that involves a reduction in established velocity. Acceleration (as well as deceleration) is a vector quantity (it has magnitude and direction). There are three types of acceleration: linear acceleration, a change of speed without change in direction; radial acceleration, a change in direction without a change of speed; and angular acceleration, a change in speed and direction. During flight, aircraft are capable of manoeuvring in all three directions, and crew and passengers may experience linear, radial and angular accelerations. In aviation, applied accelerations are commonly expressed as multiples of the acceleration due to gravity. By convention, G is the unit expressing the ratio of an applied acceleration to the gravitational constant (Glaister 1988a; Leverett and Whinnery 1985).
Biodynamics is the science dealing with the force or energy of living matter and is a major area of interest within the field of aerospace medicine. Modern aircraft are highly manoeuvrable and capable of flying at very high speeds, causing accelerative forces upon the occupants. The influence of acceleration upon the human body depends upon the intensity, rate of onset and direction of acceleration. The direction of acceleration is generally described by the use of a three-axis coordinate system (x, y, z) in which the vertical (z) axis is parallel to the long axis of the body, the x axis is oriented from front to back, and the y axis oriented side to side (Glaister 1988a). These accelerations can be categorized into two general types: sustained and transitory.
The occupants of aircraft (and spacecraft operating in the atmosphere under the influence of gravity during launch and re-entry) commonly experience accelerations in response to aerodynamic forces of flight. Prolonged changes in velocity involving accelerations lasting longer than 2 seconds may result from changes in an aircraft’s speed or direction of flight. The physiological effects of sustained acceleration result from the sustained distortion of tissues and organs of the body and changes in the flow of blood and distribution of body fluids (Glaister 1988a).
Positive or headward acceleration along the z axis (+Gz) represents the major physiological concern. In civil air transportation, Gz accelerations are infrequent, but may occasionally occur to a mild degree during some take-offs and landings, and while flying in conditions of air turbulence. Passengers may experience brief sensations of weightlessness when subject to sudden drops (negative Gz accelerations), if unrestrained in their seats. An unexpected abrupt acceleration may cause unrestrained aircrew or passengers to be thrown against internal surfaces of the aircraft cabin, resulting in injuries.
In contrast to civil transport aviation, the operation of high- performance military aircraft and stunt and aerial spray planes may generate significantly higher linear, radial and angular accelerations. Substantial positive accelerations may be generated as a high-performance aircraft changes its flight path during a turn or a pull-up manoeuvre from a steep dive. The +Gz performance characteristics of current combat aircraft may expose occupants to positive accelerations of 5 to 7 G for 10 to 40 seconds (Glaister 1988a). Aircrew may experience an increase in the weight of tissues and of the extremities at relatively low levels of acceleration of only +2 Gz. As an example, a pilot weighing 70 kg who performed an aircraft manoeuvre which generated +2 Gz would experience an increase of body weight from 70 kg to 140 kg.
The cardiovascular system is the most important organ system for determining the overall tolerance and response to +Gz stress (Glaister 1988a). The effects of positive acceleration on vision and mental performance are due to decreases in blood flow and delivery of oxygen to eye and brain. The capability of the heart to pump blood to the eyes and brain is dependent upon its capability to exceed the hydrostatic pressure of blood at any point along the circulatory system and the inertial forces generated by the positive Gz acceleration. The situation may be likened to that of pulling upward a balloon partially full of water and observing the downward distension of the balloon because of the resultant inertial force acting upon the mass of water. Exposure to positive accelerations may cause temporary loss of peripheral vision or complete loss of consciousness. Military pilots of high- performance aircraft may risk development of G-induced blackouts when exposed to rapid onset or extended periods of positive acceleration in the +Gz axis. Benign cardiac arrhythmias frequently occur following exposure to high sustained levels of +Gz acceleration, but usually are of minimal clinical significance unless pre-existing disease is present; –Gz acceleration seldom occurs because of limitations in aircraft design and performance, but may occur during inverted flight, outside loops and spins and other similar manoeuvres. The physiological effects associated with exposure to –Gz acceleration primarily involve increased vascular pressures in the upper body, head and neck (Glaister 1988a).
Accelerations of sustained duration which act at right angles to the long axis of the body are termed transverse accelerations and are relatively uncommon in most aviation situations, with the exception of catapult and jet- or rocket-assisted take-offs from aircraft carriers, and during launch of rocket systems such as the space shuttle. The accelerations encountered in such military operations are relatively small, and usually do not affect the body in a major fashion because the inertial forces act at right angles to the long axis of the body. In general, the effects are less pronounced than in Gz accelerations. Lateral acceleration in ±Gy axis are uncommon, except with experimental aircraft.
The physiological responses of individuals to transitory accelerations of short duration are a major consideration in the science of aircraft accident prevention and crew and passenger protection. Transitory accelerations are of such brief duration (considerably less than 1 second) that the body is unable to attain a steady-state status. The most common cause of injury in aircraft accidents results from the abrupt deceleration that occurs when an aircraft impacts the ground or water (Anton 1988).
When an aircraft impacts the ground, a tremendous amount of kinetic energy applies damaging forces to the aircraft and its occupants. The human body responds to these applied forces by a combination of acceleration and strain. Injuries result from deformation of tissues and organs and trauma to anatomic parts caused by collision with structural components of the aircraft cockpit and/or cabin.
Human tolerance to abrupt deceleration is variable. The nature of injuries will depend on the nature of the applied force (whether it primarily involves penetrating or blunt impact). At impact, the forces which are generated are dependent on the longitudinal and horizontal decelerations which are generally applied to an occupant. Abrupt decelerative forces are often categorized into tolerable, injurious and fatal. Tolerable forces produce traumatic injuries such as abrasions and bruises; injurious forces produce moderate to severe trauma which may not be incapacitating. It is estimated that an acceleration pulse of approximately 25 G maintained for 0.1 second is the limit of tolerability along the +Gz axis, and that about 15 G for 0.1 sec is the limit for the –Gz axis (Anton 1988).
Multiple factors affect human tolerance to short-duration acceleration. These factors include the magnitude and duration of the applied force, the rate of onset of the applied force, its direction and the site of application. It should be noted that people can withstand much greater forces perpendicular to the long axis of the body.
Physical screening of crew members to identify serious pre- existing diseases which might put them at increased risk in the aerospace environment is a key function of aeromedical programmes. In addition, countermeasures are available to crew of high-performance aircraft to protect against the adverse effects of extreme accelerations during flight. Crew members must be trained to recognize that multiple physiological factors may decrease their tolerance to G stress. These risk factors include fatigue, dehydration, heat stress, hypoglycemia and hypoxia (Glaister 1988b).
Three types of manoeuvres which crew members of high- performance aircraft employ to minimize adverse effects of sustained acceleration during flight are muscle tensing, forced expiration against a closed or partially closed glottis (back of the tongue) and positive-pressure breathing (Glaister 1988b; DeHart 1992). Forced muscle contractions exert increased pressure on blood vessels to decrease venous pooling and increase venous return and cardiac output, resulting in increased blood flow to the heart and upper body. While effective, the procedure requires extreme, active effort and may rapidly result in fatigue. Expiration against a closed glottis, termed the Valsalva manoeuver (or M-1 procedure) can increase pressure in the upper body and raise the intrathoracic pressure (inside the chest); however, the result is short lived and may be detrimental if prolonged, because it reduces venous blood return and cardiac output. Forcibly exhaling against a partially closed glottis is a more effective anti-G straining manoeuver. Breathing under positive pressure represents another method to increase intrathoracic pressure. Positive pressures are transmitted to the small artery system, resulting in increased blood flow to the eyes and brain. Positive-pressure breathing must be combined with the use of anti-G suits to prevent excessive pooling in the lower body and limbs.
Military aircrew practise a variety of training methods to enhance G tolerance. Crews frequently train in a centrifuge consisting of a gondola attached to a rotating arm which spins and generates +Gz acceleration. Aircrew become familiar with the spectrum of physiological symptoms which may develop and learn the proper procedures to control them. Physical fitness training, particularly whole-body strength training, also has been found to be effective. One of the most common mechanical devices used as protective equipment to reduce the effects of +G exposure consists of pneumatically inflated anti-G suits (Glaister 1988b). The typical trouser-like garment consists of bladders over the abdomen, thighs and calves which automatically inflate by means of an anti-G valve in the aircraft. The anti-G valve inflates in reaction to an applied acceleration upon the aircraft. Upon inflation, the anti-G suit produces a rise in the tissue pressures of the lower extremities. This maintains peripheral vascular resistance, reduces the pooling of blood in the abdomen and lower limbs and minimizes downward displacement of the diaphragm to prevent the increase in the vertical distance between the heart and brain that may be caused by positive acceleration (Glaister 1988b).
Surviving transitory accelerations associated with aircraft crashes is dependent on effective restraint systems and the maintenance of the cockpit/cabin integrity to minimize intrusion of damaged aircraft components into the living space (Anton 1988). The function of lap belts, harnesses and other types of restraint systems are to limit the movement of the aircrew or passengers and to attenuate the effects of sudden deceleration during impact. The effectiveness of the restraint system depends on how well it transmits loads between the body and the seat or vehicle structure. Energy-attenuating seating and rearward facing seats are other features in aircraft design which limit injury. Other accident-protection technology includes the design of airframe components to absorb energy and improvements in seat structures to reduce mechanical failure (DeHart 1992; DeHart and Beers 1985).
Since the 1960s, astronauts and cosmonauts have flown numerous missions into space, including 6 lunar landings by Americans. Mission duration has been from several days to a number of months, with a few Russian cosmonauts logging approximately 1-year flights. Subsequent to these space flights, a large body of literature has been written by physicians and scientists describing in-flight and post-flight physiological aberrations. For the most part, these aberrations have been attributed to exposure to weightlessness or microgravity. Although these changes are transient, with total recovery within several days to several months after returning to Earth, nobody can say with complete certitude whether astronauts would be so fortunate after missions lasting 2 to 3 years, as envisioned for a round trip to Mars. The major physiological aberrations (and countermeasures) can be categorized as cardiovascular, musculoskeletal, neurovestibular, haematological and endocrinological (Nicogossian, Huntoon and Pool 1994).
Thus far, there have been no serious cardiac problems in space, such as heart attacks or heart failure, although several astronauts have developed abnormal heart rhythms of a transient nature, particularly during extra-vehicular activity (EVA). In one case, a Russian cosmonaut had to return to Earth earlier than planned, as a precautionary measure.
On the other hand, microgravity seems to induce a lability of blood pressure and pulse. Although this does not cause impaired health or crew performance during flight, approximately half of astronauts immediately post-flight do become extremely dizzy and giddy, with some experiencing fainting (syncope) or near fainting (pre-syncope). The cause of this intolerance to being vertical is thought to be a drop in blood pressure upon re-entering the earth’s gravitational field, combined with the dysfunction of the body’s compensatory mechanisms. Hence, a low blood pressure and decreasing pulse unopposed by the body’s normal response to such physiological aberrations results in these symptoms.
Although these pre-syncopal and syncopal episodes are transient and without sequelae, there remains great concern for several reasons. First, in the event that a returning space vehicle were to have an emergency, such as a fire, upon landing, it would be extremely difficult for astronauts to rapidly escape. Second, astronauts landing on the moon after periods of time in space would be prone to some extent to pre-fainting and fainting, even though the moon’s gravitational field is one-sixth that of Earth. And finally, these cardiovascular symptoms might be far worse or even lethal after very long missions.
It is for these reasons that there has been an aggressive search for countermeasures to prevent or at least ameliorate the microgravity effects upon the cardiovascular system. Although there are a number of countermeasures now being studied that show some promise, none so far has been proven truly effective. Research has focused on in-flight exercise utilizing a treadmill, bicycle ergometer and rowing machine. In addition, studies are also being conducted with lower body negative pressure (LBNP). There is some evidence that lowering the pressure around the lower body (using compact special equipment) will enhance the body’s ability to compensate (i.e., raise blood pressure and pulse when they fall too low). The LBNP countermeasure might be even more effective if the astronaut drinks moderate amounts of specially constituted salt water simultaneously.
If the cardiovascular problem is to be solved, not only is more work needed on these countermeasures, but also new ones must be found.
All astronauts returning from space have some degree of muscle wasting or atrophy, regardless of mission duration. Muscles at particular risk are those of the arms and legs, resulting in decreased size as well as strength, endurance and work capacity. Although the mechanism for these muscle changes is still ill-defined, a partial explanation is prolonged disuse; work, activity and movement in microgravity are almost effortless, since nothing has any weight. This may be a boon for astronauts working in space, but is clearly a liability when returning to a gravitational field, whether it be that of the moon or Earth. Not only could a weakened condition impede post-flight activities (including work on the lunar surface), it could also compromise rapid ground emergency escape, if required upon landing. Another factor is the possible requirement during EVA to do space vehicle repairs, which can be very strenuous. Countermeasures under study include in-flight exercises, electrical stimulation and anabolic medication (testosterone or testosterone-like steroids). Unfortunately, these modalities at best only retard muscle dysfunction.
In addition to muscle wasting, there is also a slow but inexorable loss of bone in space (about 300 mg per day, or 0.5% of total bone calcium per month) experienced by all astronauts. This has been documented by post-flight x rays of bones, particularly of those that bear weight (i.e., the axial skeleton). This is due to a slow but unremitting loss of calcium into the urine and faeces. Of great concern is the continuing loss of calcium, regardless of flight duration. Consequently, this calcium loss and bone erosion could be a limiting factor of flight, unless an effective countermeasure can be found. Although the precise mechanism of this very significant physiological aberration is not fully understood, it undoubtedly is due in part to the absence of gravitational forces on bone, as well as disuse, similar to muscle wasting. If bone loss were to continue indefinitely, particularly over long missions, bones would become so brittle that eventually there would be risk of fractures with even low levels of stress. Furthermore, with a constant flow of calcium into the urine via the kidneys, a possibility of renal stone formation exists, with accompanying severe pain, bleeding and infection. Clearly, any of these complications would be a very serious matter were they to occur in space.
Unfortunately, there are no known countermeasures that effectively prevent calcium loss during space flight. A number of modalities are being tested, including exercise (treadmill, bicycle ergometer and rowing machine), the theory being that such voluntary physical stresses would normalize bone metabolism, thereby preventing or at least ameliorating bone loss. Other countermeasures under investigation are calcium supplements, vitamins and various medications (such as diphosphonates—a class of medications that has been shown to prevent bone loss in patients with osteoporosis). If none of these simpler countermeasures prove to be effective, it is possible that the solution lies in artificial gravity that could be produced by continuous or intermittent rotation of the space vehicle. Although such motion could generate gravitational forces similar to that of the earth, it would represent an engineering “nightmare”, in addition to major add-on costs.
More than half of the astronauts and cosmonauts suffer from space motion sickness (SMS). Although the symptoms vary somewhat from individual to individual, most suffer from stomach awareness, nausea, vomiting, headache and drowsiness. Often there is an exacerbation of symptoms with rapid head movement. If an astronaut develops SMS, it usually occurs within a few minutes to a few hours after launch, with complete remission within 72 hours. Interestingly, the symptoms sometimes recur after returning to the earth.
SMS, particularly vomiting, can not only be disconcerting to the crew members, it also has the potential to cause performance decrement in an astronaut who is ill. Furthermore, the risk of vomiting while in a pressure suit doing EVA cannot be ignored, as the vomitus could cause the life-support system to malfunction. It is for these reasons that no EVA activities are ever scheduled during the first 3 days of a space mission. If an EVA becomes necessary, for example, to do emergency repairs on the space vehicle, the crew would have to take that risk.
Much neurovestibular research has been directed toward finding a way to prevent as well as to treat SMS. Various modalities, including anti-motion-sickness pills and patches, as well as using pre-flight adaptation trainers such as rotating chairs to habituate astronauts, have been attempted with very limited success. However, in recent years it has been discovered that the antihistamine phenergan, given by injection, is an extremely effective treatment. Hence, it is carried onboard all flights and given as required. Its efficacy as a preventive has yet to be demonstrated.
Other neurovestibular symptoms reported by astronauts include dizziness, vertigo, dysequilibrium and illusions of self-motion and motion of the surrounding environment, sometimes making walking difficult for a short time post-flight. The mechanisms for these phenomena are very complex and are not completely understood. They could be problematical, particularly after a lunar landing following several days or weeks in space. As of now, there are no known effective countermeasures.
Neurovestibular phenomena are most likely caused by dysfunction of the inner ear (the semicircular canals and utricle-saccule), because of microgravity. Either erroneous signals are sent to the central nervous system or signals are misinterpreted. In any event, the results are the aforementioned symptoms. Once the mechanism is better understood, effective countermeasures can be identified.
Microgravity has an effect upon the body’s red and white blood cells. The former serve as a conveyor of oxygen to the tissues, and the latter as an immunological system to protect the body from invading organisms. Hence, any dysfunction could cause deleterious effects. For reasons not understood, astronauts lose approximately 7 to 17% of their red blood cell mass early in flight. This loss appears to plateau within a few months, returning to normal 4 to 8 weeks post-flight.
So far, this phenomenon has not been clinically significant, but, rather, a curious laboratory finding. However, there is clear potential for this loss of red blood cell mass to be a very serious aberration. Of concern is the possibility that with very long missions envisioned for the twenty-first century, red blood cells could be lost at an accelerated rate and in far greater quantities. If this were to occur, anaemia could develop to the point that an astronaut could become seriously ill. It is hoped that this will not be the case, and that the red blood cell loss will remain very small, regardless of mission duration.
In addition, several components of the white blood cell system are affected by microgravity. For example, there is an overall increase in the white blood cells, mainly neutrophils, but a decrease in lymphocytes. There is also evidence that some white blood cells do not function normally.
As of now, in spite of these changes, no illness has been attributed to these white blood cell changes. It is unknown whether or not a long mission will cause further decrease in numbers as well as further dysfunction. Should this occur, the body’s immune system would be compromised, making astronauts very susceptible to infectious disease, and possibly incapacitated by even minor illness that would otherwise easily be fended off by a normally functioning immunological system.
As with the red blood cell changes, the white blood cell changes, at least on missions of approximately one year, are not of clinical significance. Because of the potential risk of serious illness in-flight or post-flight, it is critical that research continue on the effects of microgravity on the haematological system.
During space flight, it has been noted that there are a number of fluid and mineral changes within the body due in part to changes in the endocrine system. In general, there is a loss of total body fluids, as well as calcium, potassium and calcium. A precise mechanism for these phenomena has eluded definition, although changes in various hormonal levels offer a partial explanation. To further confound matters, laboratory findings are often inconsistent among the astronauts who have been studied, making it impossible to discern a unitary hypothesis as to the cause of these physiological aberrations. In spite of this confusion, these changes have caused no known impairment of health of astronauts and no performance decrement in flight. What the significance of these endocrine changes are for very long flight, as well as the possibility that they may be harbingers of very serious sequelae, is unknown.
Acknowledgements: The authors would like to recognize the work of the Aerospace Medical Association in this area.
The helicopter is a very special type of aircraft. It is used in every part of the world and serves a variety of purposes and industries. Helicopters vary in size from the smallest single-seat helicopters to giant heavy-lift machines with gross weights in excess of 100,000 kg, which is about the same size as a Boeing 757. The purpose of this article is to discuss some of the safety and health challenges of the machine itself, the different missions it are used for, both civilian and military, and the helicopter’s operating environment.
The helicopter itself presents some very unique safety and health challenges. All helicopters use a main rotor system. This is the lifting body for the machine and serves the same purpose as the wings on a conventional airplane. Rotor blades are a significant hazard to people and property because of their size, mass and rotational speed, which also makes them difficult to see from certain angles and in different lighting conditions.
The tail rotor is also a hazard. It is usually much smaller than the main rotor and turns at a very high rate, so it too is very difficult to see. Unlike the main rotor system, which sits atop the helicopter’s mast, the tail rotor is often near ground level. People should approach a helicopter from the front, in view of the pilot, to avoid coming into contact with the tail rotor. Extra care should be taken to identify or remove obstacles (such as bushes or fences) in a temporary or unimproved helicopter landing area. Contact with the tail rotor can cause injury or death as well as serious damage to the property or helicopter.
Many people recognize the characteristic slap sound of a helicopter’s rotor system. This noise is encountered only when the helicopter is in forward flight, and is not considered a health problem. The compressor section of the engine produces extremely loud noise, often in excess of 140 dBA, and unprotected exposure must be avoided. Hearing protection (ear plugs and a noise attenuating headset or helmet) should be worn when working in and around helicopters.
There are several other hazards to consider when working with helicopters. One is flammable or combustible liquids. All helicopters require fuel to run the engine(s). The engine and the main and tail rotor transmissions use oil for lubrication and cooling. Some helicopters have one or more hydraulic systems and use hydraulic fluid.
Helicopters build a static electric charge when the rotor system is turning and/or the helicopter is flying. The static charge will dissipate when the helicopter touches the ground. If an individual is required to grab a line from a hovering helicopter, as during logging, external lifts or rescue efforts, that person should let the load or line touch the ground before grabbing it in order to avoid a shock.
Rescue/air ambulance. The helicopter was originally designed with rescue in mind, and one of its most widespread uses is as an ambulance. These are often found at the scene of an accident or disaster (see figure 2). They can land in confined areas with qualified medical teams on board who care for the injured at the scene while en route to a medical facility. Helicopters are also used for non-emergency flights when speed of transport or patient comfort is required.
Offshore oil support. Helicopters are used to help supply offshore oil operations. They transport people and supplies between land and platform and between platforms.
Executive/personal transport. The helicopter is used for point-to-point transportation. This is usually done over short distances where geography or sluggish traffic conditions prevent rapid ground transportation. Corporations build helipads on company property to allow easy access to airports or to facilitate transportation between facilities.
Sightseeing. The use of helicopters in the tourist industry has seen continuous growth. The excellent view from the helicopter combined with its ability to access remote areas make it a popular attraction.
Law enforcement. Many police departments and governmental agencies use helicopters for this type of work. The helicopter’s mobility in crowded urban areas and remote rural areas makes it invaluable. The largest rooftop helipad in the world is at the Los Angeles Police Department.
Film operations. Helicopters are a staple in action movies. Other types of movies and film-based entertainment are filmed from helicopters.
News gathering. Television and radio stations employ helicopters for traffic spotting and news gathering. Their ability to land at the place where the news is happening makes them a valuable asset. Many of them are also equipped with microwave transceivers so they can send their stories, live, over fairly long distances, while en route.
Heavy lift. Some helicopters are designed to carry heavy loads at the end of external lines. Aerial logging is one application of this concept. Construction and oil exploration crews make extensive use of the helicopter’s capacity for lifting large or bulky objects into place.
Aerial application. Helicopters can be fitted with spray booms and loaded to dispense herbicides, pesticides and fertilizers. Other devices can be added that allow helicopters to fight fires. They can drop either water or chemical retardants.
Rescue/aerial ambulance. The helicopter is used widely in humanitarian efforts. Many nations around the world have coast guards that engage in maritime rescue work. Helicopters are used to transport the sick and wounded from battle areas. Still others are sent to rescue or recover people from behind enemy lines.
Attack. Helicopters can be armed and used as attack platforms over land or sea. Weapon systems include machine guns, rockets and torpedoes. Sophisticated targeting and guidance systems are used to lock on to and destroy targets at longe range.
Transport. Helicopters of all sizes are used to transport people and supplies over land or sea. Many ships are equipped with helipads to facilitate offshore operations.
The Helicopter Operating Environment
The helicopter is used all over the world in a variety of ways (see, for example, figure 1 and figure 2). In addition, it is often working very near the ground and other obstructions. This requires constant vigilance from the pilots and those who work with or ride on the aircraft. By contrast, the fixed-wing aircraft environment is more predictable, since they fly (especially the commercial airplanes) primarily from airports whose airspace is tightly controlled.
Figure 1. H-46 helicopter landing in the Arizona, US, desert.
The combat environment presents special dangers. The military helicopter also operates in a low-level environment and is subject to the same hazards. The proliferation of inexpensive, hand-carried, heat-seeking missiles represents another danger to rotorcraft. The military helicopter can use the terrain to hide itself or to mask its telltale signature, but when in the open it is vulnerable to small-arms fire and missiles.
Military forces also use night vision goggles (NVG) to enhance the pilot’s view of the area in low-light conditions. While the NVGs do increase the pilot’s ability to see, they have severe operating limitations. One major drawback is the lack of peripheral vision, which has contributed to mid-air collisions.
Accident Prevention Measures
Preventive measures can be grouped into several categories. Any one prevention category or item will not, in and of itself, prevent accidents. All of them must be used in concert to maximize their effectiveness.
Operational policies are formulated in advance of any operations. They are usually provided by the company with the operating certificate. They are crafted from governmental regulations, manufacturer’s recommended guidelines, industry standards, best practices and common sense. In general, they have proven to be effective in preventing incidents and accidents and include:
The following are crucial support operations for the safe use of helicopters: