Preventing Fretting Damage Becomes Increasingly Critical As Aircraft Age

FLIGHT SAFETY FOUNDATION Aviation Mechanics Bulletin NOVEMBERÐDECEMBER 1998 Preventing Fretting Damage Becomes Increasingly Critical as Aircraft Age

Typical Fatigue Crack Location Outer or Critical Upper Upper Skin Row of Fasteners Adhesive

Stringer

Inner or Lower Skin FLIGHT SAFETY FOUNDATION Aviation Mechanics Bulletin Dedicated to the aviation mechanic whose knowledge, craftsmanship and integrity form the core of air safety. Robert A. Feeler, editorial coordinator

NovemberÐDecember 1998 Vol. 46 No. 6

Preventing Fretting Damage Becomes Increasingly Critical as Aircraft Age ...... 1 Maintenance Alerts...... 11 News & Tips ...... 14

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Patrick R. Veillette, Ph.D.

Fretting is a combined form of wear, cracks parallel to the major frac- fatigue and corrosion that can lead ture. Fretting was caused by to premature mechanical failure at movement of the bearing shell loads well below structural design within the connecting rod big- limits. It is a time-based failure that end bore. The bearing shell had will require increased attention as not been installed properly. the transport-category aircraft fleet ¥ Fretting corrosion occurred in continues to age. the propeller shaft bearings of a single-engine aircraft operated The following are examples of how in a marine environment. Pro- fretting damage can lead to aircraft peller vibratory stresses appear mishaps:1 to have been sufficient to cause the fretting. (The report did not ¥A helicopter struck terrain after say whether the damage was a connecting rod broke in its pis- found during routine mainte- ton engine. The primary fracture nance or following an accident surface contained a small area or incident.) of fretting damage. Scanning- electron microscopic examina- ¥ After the engine stopped operat- tion of the fretting area showed ing in flight, the crew of a mili- surface damage and the initia- tary aircraft was unable to restart tion of many small fatigue it because of fretting damage to the electrical system. The crew Whenever a mechanical fastener, made a successful emergency such as a rivet, is used to secure two landing. Investigators found that parts, vibratory stresses can cause the an electrical connector in the fastener to loosen, allowing small engine-starting system had mal- cyclic displacements to occur be- functioned because of fretting tween the two contacting surfaces. action from vibration-induced This is particularly common in the motion between the male pin connections between sheet metal and and the female receptacle. The fuselage frame structural members, incident-investigation board con- and in tail-section connections be- cluded that the vibration-sensitive cause of turbulent airflow. Fretting connector was not suitable for use damage also has occurred between in the aircraft; it was replaced with mating surfaces in oscillating bear- a vibration-resistant connector. ings and flexible couplings.

The basic requirements for fretting Small Vibratory are relative motions between two surfaces in contact; some mechanical Motions Can Cause load applied to the surfaces; and a Fretting load vector sufficient to cause slip between the surfaces. When viewed under magnification, no metal surface appears perfectly Fretting can result in excessive wear, smooth. Rather, surface irregularities surface fatigue, component fracture, appear as peaks and valleys. When loss of clamping pressure and jam- two metal components are placed in ming (by generated debris). Although contact under a load, the peaks (called most reports of fretting damage in- asperities) on one surface will adhere volve metals, composite materials to the asperities on another; simply and ceramic materials also are sus- speaking, the asperities become weld- ceptible to fretting damage.2,3 ed together. When the contacting surfaces are displaced by some vibratory Critical components such as flight motion, the welded areas rupture. The controls, powerplant controls and tail resulting wear produces debris.8,9 surfaces are especially susceptible to fretting damage because they are ex- Only slight motion is required to posed to the type of vibratory motions cause fretting. Vibratory (back-and- that cause fretting. Also highly sus- forth) motions as limited as 4 x 10-8 ceptible are roller bearings, clamped inch (1 x 10-7 millimeter) have been joints, pivots and a variety of other shown to cause fretting.10,11,12 This aircraft components.4,5,6,7 limited motion between the surfaces

2 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 distinguishes fretting from normal increasingly turbulent air flows over wear, which creates debris that typi- the rear fuselage and the empennage. cally is removed from the local area. Pronounced flexing of skin panels typ- Fretting involves such minute relative ically occurs at high angles-of-attack.13 movements that the debris remains in the general area of the damage and Debris resulting from the mechani- forms a “third body” between the sur- cal wear readily oxidizes because of faces. 11 the high temperatures created by friction between the surfaces. Depend- The motions can be produced by ing on the metals involved, the third mechanical sources, such as vibra- body of debris either can act as a lu- tions resonating throughout the ad- bricant and decrease the coefficient joining structure. An example is of friction between the two surfaces, powerplant vibrations that affect or act as an abrasive and exacerbate flight controls. Vibrations also can be the wear damage. caused by aerodynamic sources.13 Determining the source of the motion Debris often is pressed into the sur- sometimes can lead to a preventive faces, causing indentations and fur- measure. Finding and restricting vi- rows. The surface faults create stress brations from mechanical sources, risers that accelerate fatigue.1 (A however, are easier than finding and stress riser, also called a stress rais- restricting vibrations from aerody- er, is a material discontinuity that in- namic sources. duces a local increase in stress.) When fretting occurs between met- A significant aerodynamic source of als of different hardness, the softer airframe vibration is propeller slip- metal will deform the greatest stream (prop wash). Turbulent air- amount. flow within the prop wash strikes the fuselage and empennage, flexing Fretting fatigue cracks are propagat- skin surfaces and creating vibrations ed at very low stresses, well below between the structures. Aft fuselage the fatigue limit. The direction in and empennage are especially sus- which fatigue cracks grow depends ceptible to vibrations caused by prop upon the direction of the contact wash. stresses. The cracks grow perpendic- ular to the maximum principal stress Wing wake has a large influence on in the fretting area. While the overall the airflow over the empennage. Tur- applied loads may be small in the re- bulent flow from boundary-layer sep- gion of contact, the localized stress- aration begins at fairly low angles-of- es can be much larger, thus creating attack. As angle-of-attack increases, subsurface stress zones that will cause

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 3 accelerated fatigue-crack growth and alloys are very susceptible to various early component failure.14 forms of corrosion, including fretting corrosion. Some protection is achieved When the fretting area is exposed to with chemical surface treatments, but a corrosive environment, failure usu- such surfaces require additional main- ally occurs more rapidly and after tenance attention. fewer cycles than in a noncorrosive environment. The severity of corro- Machining, sion varies, depending on the types of metals involved, the carefulness in Heat-treating Cause their production and storage, the pres- Residual Stress ence of protective surfaces (chemical coatings, films and paint), and the fre- Conventional machining processes quency and quality of maintenance.1 and heat treatments used in manufac- turing and maintenance of materials Corrosion fatigue can decrease signif- can create substantial residual stress- icantly the number of cycles achieved es in the surface layer. (Residual stress before crack nucleation occurs (that is, is stress that remains in the structure before a crack begins to form), and after machining or heat treating.) For corrosion fatigue can accelerate the example, aggressive grinding of a fatigue-crack growth rate. Studies have component creates residual tensile shown that fretting damage is more stresses that facilitate crack growth. severe in aggressive corrosive environ- The greater the work performed on the ments (for example, warm, moist ar- surface of a component, the greater the eas near salt water and/or industrial energy stored as stress, which is an areas) than in protected environments internal force that causes distortion (a where oxygen and moisture are ex- change in dimension or shape) and cluded. Nevertheless, fretting corro- strain (deformation from stretching or sion cannot be prevented entirely by compressing). excluding a corrosive environment.14 Crack propagation (growth) is facili- The most effective method of prevent- tated by the “pulling-apart” action of ing fretting damage is to use materi- the tensile stresses, which can reduce als that are less susceptible to fatigue resistance (that is, resistance fretting damage. Because of aircraft- to progressive failure) by as much as performance factors, materials usual- 35 percent.15 ly are chosen for their high strength- to-weight qualities, rather than Residual stresses can be reduced by for their corrosion resistance. High- shot peening, which involves spray- strength, heat-treatable aluminum ing steel shot against the surface of

4 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 a metal component. Shot peening cre- below the surface is essential. Most ates compressive stress (that is, machine-induced residual stress oc- volume-reducing stress) in the sur- curs 0.0005 inch to 0.01 inch (0.0127 face of the metal; the compressive millimeter to 0.25 millimeter) below stress reduces the propagation of fa- the surface. Residual stress at the sur- tigue cracks.16 Nevertheless, the ex- face can be zero, but substantial tensive shot peening used in some stresses can be present less than 0.001 aircraft applications can produce sur- inch (0.025 millimeter) below the surface damage that outweighs the pos- face. Key indicators in the profile are itive effect of compressive stress. surface residual stress, peak tensile Shot peening is beneficial in reduc- stress, the crossover depth (where ing fretting fatigue that typically oc- compressive stress changes to tensile curs after relatively few cycles, but stress, or vice versa), maximum com- has little effect in reducing fatigue pressive stress and the depth of the that typically occurs after numerous residual stress layer. cycles.17 Corrosive Environment Although extensive shot peening can cause crack nucleation, it greatly re- Requires More Frequent tards crack propagation. Cracks appear Inspections less readily in unpeened surfaces, but they might propagate more rapidly.18 All aircraft must be examined during scheduled inspections for signs of There are several methods of determin- corrosion and to determine the con- ing the residual-stress profile. The two dition of protective coatings. Such most common methods are X-ray- examinations should be conducted diffraction analysis and layer-deflection more frequently when aircraft oper- analysis. (The former involves measur- ate in corrosive environments. ing the angle and the intensity at which X-rays are reflected by a component; Certain aircraft components require the latter involves measuring the deflec- more attention. Filler materials such tion of very thin layers shaved from as leather, paper, foam rubber and oth- the surface of a component.) X-ray- er soundproofing and insulating ma- diffraction analysis is especially valu- terials can absorb moisture, and should able in measuring residual stresses be- be inspected carefully. Structures sur- cause much smaller areas can be rounding doors (particularly landing- examined with great accuracy. gear doors), landing-gear wells, wing skins adjacent to countersunk-head Obtaining a stress profile to a depth fasteners, aluminum-faced honey- of a few thousandths of an inch comb panels, wing-to-body joints, and

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 5 structures susceptible to vibration and Nevertheless, abrasive action some- abrasion should receive particular times wears away the top layer of attention.19 oxidation, thereby exposing the unaffected underlying area. Surround- Corrosion products (appearing as ing debris on ferrous metals normally gray powder or white powder) might has a cocoa-like appearance. be seen visually, along with possible scoring and small indentations in re- A very common form of fretting gions of vibratory motion. Bubbling occurs at the junction of rivets and of paint and sheared rivet heads also sheet metal. Debris appears as dark- might indicate fretting corrosion. gray “dust” that flows downstream of the rivet. Because of this, fretting Because helicopters create consider- rivets commonly are called “smok- able vibratory motion, many of the ing rivets.” (Streaks of oil or dirt contacting surfaces must be inspect- that often emanate from rivets are ed, particularly those associated with not signs of fretting.) Aluminum al- the main-rotor-head assembly, gear- loys and plated-steel surfaces usu- boxes, tail-rotor assembly and trans- ally exhibit white or red powdery mission housing. deposits.19

Fiber-optic probes, magnifying lens- Prevention Methods es, mechanical probes, gauges, mir- rors and other visual aids can help Vary detect flaws. Materials selection is the most effec- Nondestructive-inspection tech- tive means of preventing fretting niques using X-rays, magnetic parti- damage. For example, when a rela- cles, fluorescent penetrant and tively soft metal is in contact with a ultrasound also can be used to detect harder metal, fretting can be mini- fretting fatigue. Scanning-electron mized by replacing the softer metal microscopy can detect microcracks with a harder metal. Materials should that signal the early stages of fretting, be carefully selected during design but this technique is relatively expen- and maintenance to preclude corrosive and requires extensive aircraft sion and fatigue. Materials that are downtime. especially susceptible to fretting should be avoided. Fretting manifests itself as surface pits surrounded by oxidation debris. Aluminum, a widely used material The pits usually are shallow and in aircraft design and maintenance, might appear to be fully oxidized. is susceptible to fretting. Instead of

6 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 aluminum, titanium alloys and fi- water pressures of 750Ð2,000 pounds brous reinforced thermoset compos- per square inch (53Ð141 kilograms ites are used for some structures. per square centimeter). Water temperature is nearly 200 degrees Fahren- Fretting fatigue can be reduced by heit (93 degrees Celsius). isolating components from corrosive environments. Chemical coatings, The high-velocity, heated water rap- films and paint provide protection idly dislodges and dissolves surface from corrosive agents. Protective sur- dirt, oil, grease and other contami- faces are most effective when they are nants. Some systems use cleaning kept clean and maintained intact.19 solvents to make the pressurized This becomes difficult when aircraft warm water even more effective. are operated in environments where foreign-object damage can occur. In Nevertheless, these systems can arid regions, for example, sand can force water, dirt, chemical solvents strike and crack the protective sur- and other contaminants into areas face, thus allowing corrosive agents that should remain free of them, in- to seep under the surface to the un- cluding bearings, bushed joints, ac- derlying metal. tuator seals and electrical connections. The resulting damage The use of greases or other lubricat- to these components leads to in- ing compounds also can isolate the creased maintenance costs and air- surfaces from the environment. craft downtime. Furthermore, many cleaning solvents can cause abrasion A corrosive attack can be minimized and corrosion if they are not thor- by reducing the amount of time that oughly rinsed from the aircraft; op- the corrosive agent remains in con- erators have reported corrosion and tact with the metal. Frequent clean- deterioration of roller-bearing ele- ing can remove corrosive agents. ments, bearings and bushings lined Anodizing (an electrolytic process with TFE (tetrafluoroethylene), that forms an airtight oxide film on landing gear joints, electrical com- the surface of aluminum alloys) and ponents and structural elements.20 chemical treatments can prevent further damage. Bearings are very susceptible to fretting damage that begins when direct Although cleaning is important, some impingement of pressurized water or high-pressure, hot-water systems solvents forces contaminants into the used to wash transport aircraft actu- joints, causing accelerated wear, ally can promote fretting damage. breakdown of internal surfaces and These systems typically generate corrosion of rolling elements.

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 7 High-pressure water can penetrate gear well. The contaminants form a bearing seals and initiate corrosion of corrosive layer of grime that adheres bearing surfaces. Water and chemi- to the surfaces of the gear, doors and cal solvents can be trapped in sealed wells. bearings (that is, bearings that are not designed to be relubricated). Re- Landing-gear components are made moving water and solvents from from very high-strength steels that sealed bearings is difficult. One sug- typically are covered with a thick, gested method is to purge the bear- semipermanent film or with grease. ing with grease; the bearing must be Maintaining the protective covering rotated to thoroughly coat the bear- is essential to prevent corrosion. The ing members with grease and force protective surface should be reapplied out the water.20 at regular maintenance intervals. Some parts of the landing gear are One major airplane manufacturer inaccessible, however, and are pro- recommends that direct spraying of tected only by the film or grease that water and solvents into joints and was applied during manufacture. roller elements be avoided, and that chemical cleaning solvents be ap- Therefore, protective grease on plied carefully and be manually landing-gear components should not scrubbed. Thorough rinsing should be removed. Removing the grease be done with generous amounts of will expose the components to cor- unpressurized, warm water. If pres- rosive agents. Inadvertent removal of surized washing equipment is used, the protective layer may not be dis- the manufacturer recommends that covered until damage has occurred. the spray nozzle be positioned at least three feet from the aircraft sur- Improper storage and shipping can face, and that the spray nozzle not cause small but significant changes be used to remove “stubborn” accu- to component strength and durabili- mulations.20 Stubborn grease and dirt ty. For example, galvanized sheets should be removed by manually (made of steel and covered with zinc scrubbing. by hot dipping or electroplating) can undergo fretting damage if they Landing gear and gear doors are are not separated during storage to susceptible to fretting damage that allow free access to the air, or not begins with the collection of oiled and clamped during ship- moisture, dirt, dust, grime and other ment.15 Bearings that depend on ro- contaminants on the tires. In some tation for thorough lubrication can aircraft, corrosive exhaust gases from be damaged by vibration during the auxiliary power unit also enter the shipping. Damage can be prevented

8 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 by applying a thin coat of lead on Because many transport-category air- the bearing surfaces before shipping; craft are near, or exceeding, their de- the lead is worn quickly away in sign-service objectives, time-based service.15 failures, such as fretting, will become more frequent and more severe as the A tracking and inspection process fleet ages.21♦ should be used to ensure that storage- and-shipping standards are met. References Fretting-fatigue damage is initiated 1. Wallace, W.; Hoeppner, David D. during the first few fretting cycles.8 AGARD Corrosion Handbook, Therefore, such damage can be pre- Volume I, Aircraft Corrosion: vented or reduced by restricting Causes and Case Histories. movement (slip) between contacting AGARDograph No. 278. A surfaces and creating and/or main- special report prepared at the taining an effective (lubricating) third request of the Advisory Group body between the surfaces before the for Aerospace Research and first loading cycle. Development. July 1985.

Slip can be reduced in some cases by 2. Freidrich, K. Journal of Material bringing loose fasteners to their prop- Science Volume 21 (1986); er torque values. Minimizing or elim- 1700Ð1706. inating surface motions in structures such as the empennage, however, is 3. Klaffe, D. Tribology International virtually impossible because of the Volume 22 (1989): 89Ð101. turbulent airflow. 4. Elliot, K.B.; Mabie, H.H.; Furey, If slip is unavoidable, a solid film lu- M.J.; Mitchell, L.D. A Vibration bricant or a soft-metal third body Analysis of a Bearing Cartridge (such as a shim) might prevent or re- Interface for a Fretting duce fretting. Hard coatings are a Corrosion Study. American poor choice, because they can induce Society of Mechanical Engineers surface fatigue. (ASME) No. 82-LUB-19.

Surface roughness and residual 5. Waterhouse, R.B. “Physics and stresses are important factors that Metallurgy of Fretting.” AGARD influence fretting behavior. Surface Conference Proceedings No. 161. roughness decreases a component’s Advisory Group for Aerospace resistance to general fatigue and to Research and Development, fretting fatigue.16 1974.

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 9 6. Peterson, M.B.; Geren, B.F.; 12. Kennedy, P.J.; Stallings, L.; Atwas, E.B.; Gray, S.; Murray, Peterson, M.B. “A Study of Surface S.F.; Lund, J.W.; Ling, F.F. Damage at Low-Amplitude Slip.” Analytical and Experimental ASLE Transactions Volume 27: Investigation of Gas Bearing 305Ð312. Tilting Pad Pivots. National Aeronautics and Space Admini- 13. Veillette, Patrick. “Characterization stration Contractor Report No. of the Fretting Forces Over the 72609, 1969. Empennage of a General Aviation Aircraft.” A special 7. Hoeppner, D.W. “Fretting of report prepared for Mechanical Aircraft Control Surfaces,” Engineering 620, “Fatigue and AGARD Conference Proceedings Creep in Design,” University of No. 161. Advisory Group for Utah. 1992. Aerospace Research and Development, 1974. 14. Evans, U.R. An Introduction to Metallic Corrosion. London, 8. Bowden, F.P.; Tabor, D. The England: Edward Arnold, 1981. Friction and Lubrication of 15. Krueger, F.E. “Fretting Failures.” Solids, Part I. Oxford, England: Metals Handbook, Volume 10, Oxford University Press, 1964. Failure Analysis and Prevention. Metals Park, Ohio, United States: 9. Bowden, F.P.; Tabor, D. The American Society for Metals, Friction and Lubrication of 1975. Solids, Part II. Oxford, England: Oxford University 16. Waterhouse, R.B.; Trowsdale, Press, 1964. A.J. “Residual Stress and Surface Roughness in Fretting Fatigue.” 10. Odfalk, Mikael; Vingsbo, Olof. Journal of Physics Volume 23 “Influence of Normal Force and (1992): A236ÐA239. Frequency in Fretting.” 35th STLE — ASME Tribology 17. Luo, W.; Noble, B.; Waterhouse, Conference, Oct. 16Ð19, 1989. R.B. Advances in Surface Treatment, Volume 5. Oxford, 11. Berthier, Y.; Vincent, L.; England: Pergamon Press, 1987. Godet, M. “Fretting Wear Mechanisms and their Effects 18. Fair, G.H.; Noble, B.; on Fretting Fatigue.” Journal of Waterhouse, R.B. Fatigue of Tribology Volume 110 (July Engineering Materials and 1988): 517Ð523. Structures. London, England:

10 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 Institute of Mechanical Engineers, About the Author 1986. Patrick R. Veillette earned a bache- 19. Hagenmaier, D.J.; Wendelbo, lor’s degree in aeronautical engineer- A.H.; Bar-Cohen, Y. “Aircraft ing at the U.S. Air Force Academy and Corrosion and Detection a doctorate in civil engineering at the Methods.” Materials Evaluation University of Utah. He is a profes- Volume 43: 426Ð437. sional pilot with more than 11,000 20. Egaas, D.R. “High-Pressure flight hours and has conducted sev- Washing.” Boeing Airliner eral research projects on cockpit (AprilÐJune 1988): 1Ð4. automation and human error in high- risk environments. Veillette has an 21. Duncan, Richard. “Fatigue and airline transport pilot certificate and Corrosion Tax Aging Aircraft.” is a former U.S. Federal Aviation Aerospace America (September Administration designated pilot 1991): 41. examiner.

MAINTENANCE ALERTS

NTSB Wants Improved (PIA) Boeing 747-240 shut down Containment Capability the no. 2 engine after hearing For General Electric unusual noises and seeing indi- cations of loss of oil pressure and CF6 Engines oil quantity from the CF6-50E2 engine while departing from Several uncontained failures of Gen- New York, New York, U.S. The eral Electric (GE) Aircraft Engines crew flew the airplane back to the CF6-50 and CF6-80 engines have departure airport and landed prompted the U.S. National Transpor- without further incident. NTSB tation Safety Board (NTSB) to call said that the engine fan midshaft for improved containment capability (FMS) had fractured and had for the engines. caused the low-pressure turbine (LPT) rotor to overspeed and NTSB cited the following incidents: shed blades. Debris punctured ¥ On Dec. 6, 1995, the crew of a the left-wing leading-edge slats Pakistan International Airlines and a landing-gear door.

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 11 ¥ On Jan. 24, 1996, the no. 1 en- Evacuation-slide gine on an American Airlines Separations Prompt Airbus A300-600 spooled down on departure from Philadelphia, Call to Mandate System Pennsylvania, U.S. The crew re- Modifications And turned to the departure airport Maintenance Training and landed safely. NTSB said that an interturbine-temperature Citing six incidents in which off-wing probe in the CF6-80C2A5 en- emergency-evacuation slides separat- gine had separated and had ed from B-757s in flight, NTSB has struck one LPT blade. The blade recommended that aircraft operators fractured and struck other LPT be required to modify the systems blades. The damage ruptured the according to Boeing service bulletins LPT case. (SBs) and that the FAA ensure that B-757 maintenance technicians re- ¥ On Feb. 22, 1996, the crew of a ceive training on the system modifi- Continental Airlines McDonnell cations. Douglas DC-10 rejected their takeoff from Houston, Texas, NTSB said that about half of the U.S. when the no. 3 engine B-757 fleet has off-wing emergency- surged. NTSB said that the FMS evacuation slides, which are in fuse- had fractured and caused an un- lage compartments just above the contained failure of the trailing edges of the wings. All six CF6-50C2 engine’s LPT. Debris incidents occurred soon after main- penetrated the engine-core cowl tenance was performed on the slides. but did not damage any other Some of the aircraft were damaged parts of the airplane. when the slide separations occurred, but all were landed safely. NTSB said that GE data show that 25 uncontained LPT failures have oc- The first incident occurred on June 8, curred in CF6-50 engines, and that six 1993. The United Airlines crew made uncontained LPT failures have oc- an emergency landing after the left curred in CF6-80C2 engines. NTSB slide separated at Flight Level 250. recommended that the U.S. Federal Three months later, Boeing informed Aviation Administration require GE B-757 operators about the incident, to “improve the ability of the CF6-50 which occurred because a partially and the CF6-80 series engines to pre- engaged door latch allowed the door vent fractured [LPT] blades from be- to flex and then be forced open by the ing liberated through the engine air stream. Boeing also revised the cowling.” B-757 maintenance manual to clarify

12 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 door-latching procedures and to incor- York, New York, U.S. on June 2, porate placard instructions on the 1998, when the left slide sepa- doors. rated. The flight continued to, and landed safely at, the sched- In October 1996, Boeing issued SB uled destination, Covington, 757-25-0182, which included infor- Kentucky, U.S. NTSB said that mation on two incidents that occurred the aft fuselage was substantial- after June 8, 1993, and instructions ly damaged; and, for modifying the slide system. The incidents involved a Continental Air- ¥A United Airlines airplane that lines B-757 on Sept. 25, 1995, and a was being rotated for takeoff Boeing flight-test airplane on Nov. from Seattle, Washington, U.S., 15, 1995. when the left slide separated. The flight continued to, and landed NTSB said that three recent incidents safely at, Denver, Colorado, U.S. involved airplanes that were not mod- ified according to the SB. The inci- NTSB recommended that the FAA dents involved: issue an airworthiness directive (AD) requiring compliance with SB ¥ An American Airlines airplane 757-25-0182 and issue another AD from which a slide separated on following introduction by Boeing of June 24, 1997. (The NTSB further modifications to the slide sys- safety-recommendation docu- tem. (NTSB said that Boeing expect- ment provided no further details ed to issue an SB on the new about this incident, except that modifications in December 1998.) the airline subsequently paint- ed red stripes on the slide- NTSB also said that the FAA should compartment door frames to “issue a flight standards information help mechanics determine when bulletin to require that principal main- the door is properly positioned tenance inspectors ensure that all and latched.); mechanics [who work on these air- ¥A Delta Air Lines airplane that craft] are trained on the new off-wing was departing from LaGuardia escape slide system enhancements on International Airport in New the B-757.”♦

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 13 NEWS & TIPS

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Starmet-refurbished Aircraft Counterweights

For more information: Starmet Corp., 2229 Main Street, Concord, MA 01742 U.S. Telephone +(978) 369- Menu screen of Lube-It 2.5ª 5410. for Windows

14 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 Parts Washer Uses For more information: SystemOne Self-contained Clean Technologies, Suite 107, 8305 N.W. 27th Street, Miami, FL 33122 U.S. Solvent Recycling Telephone +(305) 593-8015. The SystemOne¨ Model 500 recy- Air-purifying cling general-parts washer uses a low- temperature vacuum-distillation and Respirators Provide recovery process that recycles solvent Wide Field of Vision without off-site processing, according to the manufacturer. The self- The WillsonMaxª 8000 Series of contained washer removes all con- full-facepiece, air-purifying respira- taminants from dirty solvent, mini- tors provides the industry’s widest mizes waste by-product volume, and field of vision, according to the man- eliminates the need for transportation ufacturer. Also designed for safety- of large quantities of hazardous, dirty standard compliance and wearer solvent, said the company. The Mod- comfort/acceptance, the respirators el 500 has a 36-inch by 27-inch by provide unobstructed peripheral vi- 9.5-inch (91 centimeter [cm] by 69 sion and eliminate tunnel vision and cm by 24 cm) sink work area. blind spots, said the company. Anti- fog coating, a speech transmitter, and an oral-nasal mask to help eliminate fogging and carbon-dioxide buildup are among the features of various models. The respirators are said to meet U.S. standards for air filtration, impact protection and optical clarity.

For more information: Dalloz Safe- ty, Second and Washington Streets, P.O. Box 622, Reading, PA 19603- 0622 U.S. Telephone +(610) 376- 6161 Nylon Cable Wrap Is Self-extinguishing, Nontoxic

SystemOne¨ Model 500 A line of spirally-cut nylon cable Parts Washer wrap and chafe guard is designed for

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 15 use in enclosed environments where Compliance Guide for Managers of the possibility of fire exists. Heli- Motor Vehicle/Equipment Mainte- Tube¨ produces no toxic or irritating nance and Refueling Operations was by-products when exposed to open written for shop managers and cov- flame or heated to high operating ers OSHA regulations, including temperatures, according to the man- those for hazardous materials, asbes- ufacturer. The wrap accommodates tos brake-dust control, emergency bundles from 1/16 inch (0.16 centi- planning and first aid. The guide also meter) outside diameter to seven contains a directory of federal and inches (17.8 centimeters) outside di- state OSHA offices, state fire mar- ameter, is unaffected by solvents, shals, and Canadian workplace- alkalis and most acids, and operates safety agencies. at temperatures from Ð121 degrees Fahrenheit (F; Ð85 degrees Celsius For more information: Environmen- [C]) to 200 degrees F (93 degrees C), tal Development Corporation, P.O. said the manufacturer. Technical Box 854, Findlay, OH 45839-0854 specifications are available for abra- U.S. Telephone +(419) 422-1200. sion resistance, flammability and ver- sions resistant to ultraviolet light. Kit Indicates Water in Aviation Fuels For more information: M. M. New- man Corp., 24 Tioga Way/P.O. Box The CDF (Clean Dry Fuel) water- 615, Marblehead, MA 01945 U.S. indicator-pad kit indicates the pres- Telephone +(781) 631-7100. ence of undissolved water in mobile or stationary aviation fuel-tank sys- Compliance Guide tems, according to the manufacturer. Covers Vehicle Testing requires a small fuel sample Maintenance, Refueling taken in a test cap from the fuel nozzle or the lowest point of a tank sump. A new guide to shop safety and A chemically treated pad is dropped compliance with U.S. Occupational into the fuel sample and yields a Safety and Health Administration visual positive or negative result in (OSHA) guidelines covers all of the approximately one minute. materials, equipment, tools and jobs in motor vehicle maintenance-and- For more information: AVFMATS, refueling operations, according to P.O. Box 8803, Columbus, GA 31908 the publisher. Shop Safety/OSHA U.S. Telephone +(706) 327-0909.♦

16 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ NOVEMBERÐDECEMBER 1998 BLANK INSIDE BACK COVER Flight Safety Foundation

11th annual European Aviation Safety Seminar (EASS)

“Flight Safety: Management, Measurement and Margins” March 8–10, 1999 Grand Hotel Krasnapolsky, Amsterdam, Netherlands Among the topics are propulsion system malfunction; rushed and unstabilized approaches; and alertness technology: medication, diet and the scientific findings

For registration information: Flight Safety Foundation, Suite 300, 601 Madison Street, Alexandria, VA 22314 U.S. Telephone: +(703) 739-6700 Fax: +(703) 739-6708 Joan Perrin, director of marketing and development, ext. 109

Visit our World Wide Web site at http://www.flightsafety.org