Cameron, Buck

Cameron, Buck

Address: Carpenters Health and Safety Fund, 7016 46th Avenue SW, Seattle, Washington 98136

Country: United States

Phone: 1 (206) 935-7748

Fax: 1 (206) 935-7808

E-mail: buckcamron@aol.com

Past position(s): Industrial Hygienist, IAM District 751; Industrial Hygienist/Business Representative, Teamster Airline Division

Education: BA, 1969, University of San Francisco; BS, 1977, University of California, Berkeley; MS, 1982, University of California, Berkeley

Areas of interest: Workplace health and safety in construction and aerospace; heat stress

Thursday, 31 March 2011 17:32

Aircraft Maintenance Operations

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.

 

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Wednesday, 23 February 2011 16:13

The Aerospace Industry

General Profile

History and future trends

When Wilbur and Orville Wright made their first successful flight in 1903, aircraft manufacturing was a craft practised in the small shops of experimenters and adventurers. The small but dramatic contributions made by military aircraft during the First World War helped to take manufacturing out of the workshop and into mass production. Second-generation aircraft helped post-war operators to make inroads into the commercial sphere, particularly as carriers of mail and express cargo. Airliners, however, remained unpressurized, poorly heated and unable to fly above the weather. Despite these drawbacks, passenger travel increased by 600% from 1936 to 1941, but was still a luxury that relatively few experienced. The dramatic advances in aeronautical technology and the concomitant use of air power during the Second World War fostered the explosive growth of aircraft manufacturing capacity that survived the war in the United States, the United Kingdom and the Soviet Union. Since the Second World War, tactical and strategic missiles, reconnaissance and navigational satellites and piloted aircraft have taken on ever greater military significance. Satellite communication, geo-monitoring and weather-tracking technology have become of increasing commercial importance. The introduction of turbojet-powered civilian aircraft in the late 1950s made air travel faster and more comfortable and began a dramatic growth in commercial air travel. By 1993 over 1.25 trillion passenger miles were flown worldwide annually. This figure is projected to nearly triple by 2013.

Employment patterns

Employment in aerospace industries is highly cyclical. Direct aerospace employment in the European Union, North America and Japan peaked at 1,770,000 in 1989 before decreasing to 1,300,000 in 1995, with much of the employment loss occurring in the United States and the United Kingdom. The large aerospace industry in the Confederation of Independent States has been significantly disrupted subsequent to the break-up of the Soviet Union. Small but rapidly growing manufacturing capability exists in India and China. Manufacture of intercontinental and space missiles and long-range bombers has been largely restricted to the United States and the former Soviet Union, with France having developed commercial space launch capabilities. Shorter-range strategic missiles, tactical missiles and bombers, commercial rockets and fighter aircraft are more widely manufactured. Large commercial aircraft (those with 100 or greater seat capacity) are built by, or in cooperation with, manufacturers based in the United States and Europe. The manufacture of regional aircraft (less than 100 seat capacity) and business jets is more dispersed. The manufacture of aircraft for private pilots, based primarily in the United States, decreased from nearly 18,000 aircraft in 1978 to fewer than 1,000 in 1992 before rebounding.

Employment is divided in roughly equal measures among the manufacture of military aircraft, commercial aircraft, missiles and space vehicles and related equipment. Within individual enterprises, engineering, manufacturing and administrative positions each account for approximately one-third of the employed population. Males account for about 80% of the aerospace engineering and production workforce, with the overwhelming majority of highly skilled craftspeople, engineers and production managers being male.

Industry divisions

The markedly different needs and practices of governmental and civilian customers typically result in the segmentation of aerospace manufacturers into defense and commercial companies, or divisions of larger corporations. Airframes, engines (also called powerplants) and avionics (electronic navigational, communication and flight control equipment) are generally supplied by separate manufacturers. Engines and avionics each may account for one-quarter of the final cost of an airliner. Aerospace manufacturing requires the design, fabrication and assembly, inspection and testing of a vast array of components. Manufacturers have formed interconnected arrays of subcontractors and external and internal suppliers of components to meet their needs. Economic, technological, marketing and political demands have led to an increasing globalization of the manufacture of aircraft components and sub-assemblies.

Manufacturing Materials, Facilities and Processes

Materials

Airframes were originally made from wood and fabric, and then evolved to metal structural components. Aluminium alloys have been widely used due to their strength and light weight. Alloys of beryllium, titanium and magnesium are also used, particularly in high-performance aircraft. Advanced composite materials (arrays of fibre embedded in plastic matrices) are a family of strong and durable replacements for metallic components. Composite materials offer equal or greater strength, lower weight and greater heat resistance than currently used metals and have the additional advantage in military aircraft of significantly reducing the radar profile of the airframe. Epoxy resin systems are the most commonly used composites in aerospace, representing about 65% of materials used. Polyimide resin systems are used where high temperature resistance is required. Other resin systems used include phenolics, polyesters and silicones. Aliphatic amines are often used as curing agents. Supporting fibres include graphite, Kevlar and fibreglass. Stabilizers, catalysts, accelerators, antioxidants and plasticizers act as accessories to produce a desired consistency. Additional resin systems include saturated and unsaturated polyesters, polyurethanes and vinyl, acrylic, urea and fluorine-containing polymers.

Primer, lacquer and enamel paints protect vulnerable surfaces from extreme temperatures and corrosive conditions. The most common primer paint is composed of synthetic resins pigmented with zinc chromate and extended pigment. It dries very rapidly, improves adhesion of top coats and prevents corrosion of aluminium, steel and their alloys. Enamels and lacquers are applied to primed surfaces as exterior protective coatings and finishes and for colour purposes. Aircraft enamels are made of drying oils, natural and synthetic resins, pigments and appropriate solvents. Depending on their application, lacquers may contain resins, plasticizers, cellulose esters, zinc chromate, pigments, extenders and appropriate solvents. Rubber mixtures find common use in paints, fuel cell lining materials, lubricants and preservatives, engine mountings, protective clothing, hoses, gaskets and seals. Natural and synthetic oils are used to cool, lubricate and reduce friction in engines, hydraulic systems and machine tools. Aviation gasoline and jet fuel are derived from petroleum-based hydrocarbons. High-energy liquid and solid fuels have space flight applications and contain materials with inherently hazardous physical and chemical properties; such materials include liquid oxygen, hydrazine, peroxides and fluorine.

Many materials are used in the manufacturing process which do not become part of the final airframe. Manufacturers may have tens of thousands of individual products approved for use, although far fewer are in use at any time. A large quantity and variety of solvents are used, with environmentally damaging variants such as methyl ethyl ketone and freon being replaced with more environmentally friendly solvents. Chromium- and nickel-containing steel alloys are used in tooling, and cobalt- and tungsten carbide-containing hard-metal bits are used in cutting tools. Lead, formerly used in metal-forming processes, is now rarely used, having been replaced with kirksite.

In total, the aerospace industry uses more than 5,000 chemicals and mixtures of chemical compounds, most with multiple suppliers, and with many compounds containing between five and ten ingredients. The exact composition of some products is proprietary, or a trade secret, adding to the complexity of this heterogeneous group.

Facilities and manufacturing processes

Airframe manufacturing typically is done in large, integrated plants. Newer plants often have high-volume exhaust ventilation systems with controlled make-up air. Local exhaust systems may be added for specific functions. Chemical milling and large component painting are now routinely performed in closed, automated ranks or booths that contain fugitive vapour or mist. Older manufacturing facilities may provide much poorer control of environmental hazards.

A large cadre of highly trained engineers develop and refine the structural characteristics of the aircraft or space vehicle. Additional engineers characterize the strength and durability of component materials and develop effective manufacturing processes. Computers have taken on much of the calculating and drafting work that was previously performed by engineers, drafters and technicians. Integrated computer systems can now be used to design aircraft without the aid of paper drawings or structural mock-ups.

Manufacturing begins with fabrication: the making of parts from stock materials. Fabrication includes tool and jig making, sheet-metal working, machining, plastic and composite working and support activities. Tools are built as templates and work surfaces on which to construct metal or composite parts. Jigs guide cutting, drilling and assembly. Fuselage sub-sections, door panels and wing and tail skins (outer surfaces) are typically formed from aluminium sheets that are precisely shaped, cut and chemically treated. Machine operations are often computer controlled. Huge rail-mounted mills machine wing spars from single aluminium forgings. Smaller parts are precisely cut and shaped on mills, lathes and grinders. Ducting is formed from sheet metal or composites. Interior components, including flooring, are typically formed from composites or laminates of thin but rigid outer layers over a honeycomb interior. Composite materials are laid up (put into carefully arranged and shaped overlapping layers) by hand or machine and then cured in an oven or autoclave.

Assembly begins with the build-up of component parts into sub-assemblies. Major sub-assemblies include wings, stabilizers, fuselage sections, landing gear, doors and interior components. Wing assembly is particularly intensive, requiring a large number of holes to be precisely drilled and counter-sunk in the skins, through which rivets are later driven. The finished wing is cleaned and sealed from the inside to ensure a leak-proof fuel compartment. Final assembly takes place in huge assembly halls, some of which are among the world’s largest manufacturing buildings. The assembly line comprises several sequential positions where the airframe remains for several days to more than a week while predetermined functions are performed. Numerous assembly operations take place simultaneously at each position, creating the potential for cross exposures to chemicals. Parts and sub-assemblies are moved on dollies, custom-built carriers and by overhead crane to the appropriate position. The airframe is moved between positions by overhead crane until the landing and nose gear are installed. Subsequent movements are made by towing.

During final assembly, the fuselage sections are riveted together around a supporting structure. Floor beams and stringers are installed and the interior coated with a corrosion-inhibiting compound. Fore and aft fuselage sections are joined to the wings and wing stub (a box-like structure that serves as a main fuel tank and the structural center of the aircraft). The fuselage interior is covered with blankets of fibreglass insulation, electrical wiring and air ducts are installed and interior surfaces are covered with decorative panelling. Storage bins, typically with integrated passenger lights and emergency oxygen supplies, are then installed. Pre-assembled seating, galleys and lavatories are moved by hand and secured to floor tracks, permitting the rapid reconfiguration of the passenger cabin to conform to air carrier needs. Powerplants and landing and nose gear are mounted, and avionic components are installed. The functioning of all components is thoroughly tested prior to towing the completed aircraft to a separate, well-ventilated paint hanger, where a protective primer coat (normally zinc-chromate based) is applied, followed by a decorative top-coat of urethane or epoxy paint. Prior to delivery the aircraft is put through a rigorous series of ground and flight tests.

In addition to workers engaged in the actual engineering and manufacturing processes, many employees are engaged in planning, tracking and inspecting work and expediting the movement of parts and tools. Craftspeople maintain power tools and reface cutting bits. Large staffs are needed for building maintenance, janitorial services and ground vehicle operation.

 

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