Combat Fatigue

Air combat simulation T-34s found to have extensive fatigue cracking


The following information is derived from the FAAs Service Difficulty Reports and Aviation Maintenance Alerts. Click here to view “Airworthiness Directives.”


Following on the heels of an airworthiness directive and an earlier warning about aerobatic flight, the FAA is continuing its investigation into fatigue on T-34s used in air combat simulation.

After the April 1999 accident that followed the in-flight wing separation of a T-34A Mentor, a metallurgic examination found structural fatigue cracks at several of the fracture surfaces. An examination of the left wing, which did not separate from the airplane, also displayed fatigue cracks at several locations, the FAA says.

The accident aircraft had accumulated about 8,200 flight hours, the last 4,000 of which were in simulated air combat operations.

Because this was the first known occurrence of a wing failure in a T-34, the FAA has concluded that simulated air combat flights accelerate the development of structural fatigue.

The FAA has therefore recommended that operators create a structural inspection program to maintain the airworthiness of each aircraft used in simulated air combat flights.

Operators are also being urged to consider measures to reduce the severity of structural fatigue loads, including placing limits on maximum load factor or maximum air combat speed.

The FAA also stressed that other aircraft used in simulated air combat, including the Extra 300, the SIAI-Marchetti SF-260 and the T-6/SNJ should also follow these protocols.

Beech F33A Bonanza
Flap Track Wear

During a scheduled inspection, the technician discovered that both inboard flap tracks were severely worn.The flap rollers had worn into the side of each flap track and caused irreparable damage. The technician said this was the fourth time he found damaged flap tracks out of five similar airplanes he had inspected in the previous three months. Two of the four damaged pairs had repairable damage; however, he had to replace the other two pairs of flap track.Part total time – 1,995 hours.

Beech A36 Bonanza
Alternator Failure

The owner reported an electrical burning odor in the area of the engine cowling.The alternator had seized and the drive was sheared. The alternator had been installed a short time prior to this occurrence. Approximately 2 weeks prior, the technician found a similar defect on another like aircraft with 120 operating hours since installation of the alternator.The FAA Service Difficulty Reporting Program data base contains seven additional reports of alternator drive failure. These additional failures occurred on three Beech A36 and four Cessna 421C aircraft.Part total time – 10 hours.

Beech 58 Baron
Nose Landing Gear Defect

After takeoff, the pilot retracted the landing gear. The transit light remained on and he heard a loud pop. He extended the landing gear and made a safe landing.A technician discovered that the rod-end broke on the drag brace end of the nose gear retraction rod. The rod-end outer case failed and distorted into an egg shape at the grease zerk. This allowed the rod-end bearing to separate from the outer case.Part total time – 6,000 hours.

Beech C-90 King Air
Main Landing Gear Defect

During the landing roll, the aircraft pulled to the right and went off the runway.An investigation disclosed the right main landing gear torque knee had broken. The upper half of the torque knee assembly had cracked and broken at three locations. This failure allowed the main gear wheel assembly to rotate on the lower section of the strut.The torque knee assembly is constructed of aluminum. Beech issued Service Bulletin 32-3134 giving an inspection procedure and stating that replacement torque knee parts will be constructed of a steel alloy. For specific aircraft applicability consult SB 32-3134.Part total time – 170 hours.

Cessna 172R Skyhawk
Brake Fluid Leakage

Both main landing gear brake assemblies were found to be leaking.Both brake lines were found to be leaking at the lowest point, just inboard of the brake calipers. Pin holes that appeared to be corrosion-induced were found in each line. The brake lines are encased in a factory-installed plastic sleeve that did not have weep holes.Part total time – 452 hours.

Cessna 172R Skyhawk
Electrical System Failure

The pilot reported that the alternator out light illuminated and the amp meter indicated zero during flight. He cycled the alternator switch and the out light stayed off. However, the amp meter went to full charge.He made an uneventful precautionary landing. The alternator control unit was heat-damaged and the case was partially melted. The wiring attached to the alternator control unit was burned and displayed evidence of arcing. Additionally, the electrical power junction box displayed evidence of extreme heat and smoke damage.Part total time – 686 hours.

Cessna 180A Skywagon
Hose Deterioration

During an annual inspection, the technician discovered severely deteriorated brake hoses.Both of the brake master cylinders flexible hoses were stiff, brittle and seeping fluid. The hoses had apparently been neglected for a long period of time, and total failure of one or both brake hoses was imminent. Part total time – 7,675 hours.

Cessna 441 Conquest
Bleed Air Leak, Electrical Short

While investigating the cause of an ADF problem, the technician discovered that arcing of electrical wires had burned a hole in a bleed air tube.The power wires for the right electrical buss were routed over a bulkhead at fuselage station 130 and under a bleed air tube. Four wires were welded to the bleed air tube and had burned a hole in it. The covering on an adjacent antenna coax wire melted due to excessive heat caused by escaping bleed air.Part total time – 16,447 hours.

Grumman Americans AA-1B, AA-1C, AA-5 and AA-5B
Safety Belt AD

While conducting an annual inspection, the technician discovered safety belts installed that were not in compliance with AD 79-16-02.The technician said it was the third set of noncompliant safety belts he had found in the past year. The safety belts covered by AD 79-16-02 were distributed by Indiana Mills And Manufacturing. AD 79-16-02 was effective August 2, 1979; therefore, it is apparent these safety belts were overlooked during many past inspections.Part total time – 1,132 hours.

Mooney M20E Chaparral
Wing Spar Damage

During an annual inspection, a maintenance technician discovered damage on the left outboard wing. While replacing the outboard wing assembly, the technician found severe wing spar corrosion.Intergranular corrosion attacked the lower spar cap on the stub spar from wing station 33 outboard. The spar cap damage was well beyond repairable limits and the part was replaced. The structural integrity of the left wing was seriously compromised by this defect and could have allowed in-flight separation of the outer wing section.Part total time – 3,503 hours.

Piper PA-23-250 Aztec
Landing Gear Failure

When the pilot selected the landing gear to the down position, he lost primary hydraulic system pressure and the gear remained in the up position. He used the emergency CO2 gear extension system and the auxiliary hand pump, but the gear failed to extend and the airplane was landed gear up.An inspection revealed that a hydraulic line attached to the left landing gear sequence valve had been chafed by the left rudder cable. When the hydraulic line was penetrated, all the primary hydraulic system fluid escaped, depleting the system. When the emergency system was activated, the cable housing to the priority valve slipped, causing insufficient pressure to pull the pin on the priority valve.The use of the auxiliary hand pump depleted any remaining hydraulic fluid.Part total time – 9,516 hours.

Piper PA-28-180 Cherokee
Electrical System Failure

The pilot experienced a total electrical system failure during a ground run-up.A mechanic found the electrical wire from the alternator (battery) terminal to the main buss at the circuit breaker panel was chafed and shorted to a metal line. The electrical short welded the wire to the number 1 cylinder primer line. Although the primer line was not penetrated, a serious fire hazard explosion hazard existed.

Piper PA-28-235 Pathfinder
Rudder Control System Cracks

During an annual inspection, the technician discovered cracks in the rudder control system.Both of the lower front corners of the rudder pedal support were cracked. The cracks ran from the edge of the support to the front mount bolt holes. The cracks may have resulted from the front two mount bolts not being properly torqued when they were installed. Part total time – 2,268 hours.

Piper PA-32R-301T Turbo Saratoga
Reduced Engine Performance

After a flight, the pilot reported that the manifold pressure suddenly dropped.During an inspection, the technician discovered that the engine air intake tube was broken where an adapter elbow was attached. The adapter elbow was welded to the air inlet tube, and the crack developed adjacent to the weld. The reduction in manifold pressure was attributed to a 1-inch diameter hole in the air inlet tube that resulted from the separation of the adapter. Part total time – 19 hours.


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