Strut Protection

Spring steel landing gear struts need care to handle abuse


The following information is derived from the FAAs Service Difficulty Reports and Aviation Maintenance Alerts.


The NTSB has recommended that initial and repetitive non-destructive inspections be accomplished on main landing gear spring struts of Cessna tailwheel airplanes.

These recommendations stem from an investigation of an accident in which the main gear spring failed at the upper axle attachment to the spring strut. This particular spring strut underwent major repair for previous damage prior to this accident.

FAA Service Difficulty Reports indicate that failures can occur in the gear spring struts at the axle attachment. Generally, such failures occur from corrosion pits in or at the axle attach points when the spring struts are modified for skis or oversized tires.

Failures have occurred in other areas of the spring strut due to corrosion that has penetrated the shot-peened layer. Corrosion can occur where nicks and gouges have penetrated the paint or where close fitting parts retain moisture. Wear between the spring and the landing gear support fittings can also penetrate the shot-peened layer if the wedges are allowed to get loose. Corrosion nicks or gouges can lead to failure during hard landingsVisual inspections of the spring strut should be performed every 50 hours and during annual inspections, as required by the maintenance manuals. Nicks and gouges should be sanded lightly to remove corrosion, taking care not to exceed the depth of the shot-peened layer. Refinishing will then protect against corrosion.

This is particularly important when the airplanes are modified for the installation of skis and oversized tires. Check for rust, nicks, gouges and other surface damage. Whenever repairs are made, the underside of the strut must be shot-peened.

Alignment of the landing gears is difficult on these airplanes, but alignment must be done properly to minimize damage due to hard landings. Wheels can be aligned using shims, but do not attempt to align the wheels by bending the strut.

Beech E18S Twin Beech
Poor Engine Performance

After takeoff, the pilot noticed the right engine would not produce climb power. He returned to the departure airport and landed the aircraft safely.The engines installed on this aircraft were Pratt & Whitney R-985s. The technician found the engine ignition harness contained enough water to partially ground out the ignition system.Engine total time – 1,243 hours.

Beech C-23 Sundowner
Defective Fuel Selector Valve

While complying with the requirements of AD 75-01-04, the technician discovered the fuel selector valve did not function properly.It took 25 inch-pounds of torque to turn the selector valve, but the required limit is 5 inch-pounds. He disassembled the fuel selector valve and found the valve cone was severely scored.Part total time – 3,296 hours.

Beech F33A Bonanza
Fuel Odor in the Cabin

During a landing approach, the odor of fuel was detected in the cabin.A technician discovered the engine-driven fuel pump was leaking from the case drain. This fuel pump may have been defective when it was manufactured.Part total time – 434 hours.

Beech A36 Bonanza
Defective Landing Gear Actuator

During a scheduled inspection, the technician conducted a landing gear retraction test and discovered a defect.With the gear handle selected up, it retracted normally. However, with the gear selected down, the gear actuator jammed in the up position. The landing gear motor failed immediately. All of the safety switches and the dynamic brake relay were properly rigged and functioning correctly. Part total time – 93 hours.

Beech E90 King Air
Aileron Structural Defect

While complying with Beech service bulletin 57-3148, the technician discovered a crack on the top skin of the aileron just outboard of the inboard hinge point. The crack was approximately 4.5 inches long and ran parallel to a skin lap joint. The crack was concealed by the paint and could not be found until the paint was removed.Part total time – 9,447 hours.

Beech 95 Travel Air
Nose Gear Collapse

The nose landing gear collapsed during a landing rollout.A technician discovered the landing gear crank arm was cracked. The weight of the nose gear may have applied enough pressure to the push-pull rod that the crank arm rotated and released the nose gear. Metal fatigue is the most probable cause for this failure. The same landing gear arrangement is used on many other Beech aircraft models.

Cessna 172N Skyhawk
Main Landing Gear Failure

During a landing, the right main landing gear failed.A technician found a right gear leg spring attachment bolt broken, which allowed the gear leg to rotate approximately 180 degrees. While interviewing the pilot, the technician learned this damage may have been caused by exceptionally hard braking. Part total time – 9,601 hours.

Cessna 172P Skyhawk
Flight Control Linkage Damage

During an annual inspection, the technician found the elevator control yoke damaged.The yoke was full of rusty water and the interior of the tube assembly was severely corroded. Cessna service bulletin SEB-01-3 allows drilling a hole in the elevator control yoke tubing for recurring inspections and drainage. When the inspection/drain hole was drilled in the control yoke tube, the rusty water poured out.Part total time – 8,300 hours.

Cessna 177RG Cardinal
Structural Corrosion

To accommodate installation of a shoulder harness kit, the technician removed the cabin headliner and found severe structural corrosion.The corrosion-damaged areas were the forward and aft upper spar caps and skins on both sides of the center wing section. He also discovered a crack in the left wing root rib and severe corrosion in the left and right wing root rib assemblies.

Cessna U206G Stationair
Flight Control Interference

After an accident, the pilot stated he had experienced uncontrollable pitch control and limited aileron control immediately after takeoff.An investigator discovered an electrical cable assembly had fouled the control column bearing assembly. The electrical cable was jammed between the rollers and the control tube, which prevented elevator control and severely limited aileron control.The submitter owns and operates one additional like aircraft. He inspected the aircraft and found similar damage on the same flight control interference.

Cessna TU206G Turbo Stationair
Wheel Brake Failure

The pilot reported the left wheel brake failed while taxiing to the runway.A technician found the master cylinder lower attachment brackets were broken. This finding prompted him to inspect another like aircraft, on which the brackets were badly bent.Part total time – 3,359 hours.

Cessna 421C Golden Eagle
Hydraulic Pump Failure

During a 25-hour engine oil change, the technician noticed oil venting out of the right engine overboard drain and the oil had a metallic glimmer.The technician removed the oil filter but did not find evidence of excessive metal contamination. He traced the source of the venting oil to the engine-driven hydraulic pump at the accessory drive case. He discovered the bearing in the drive adapter was seized to the drive shaft, which allowed it to spin inside the housing. The seized bearing deposited a significant amount of bronze and aluminum into the oil sump through the accessory case and produced enough heat to melt the rear shaft seal, which allowed the oil to vent overboard.Part total time – 239 hours.

Hartzell HC-C2YL-2CUF Propeller
Feathering Defect

This propeller is installed on a Piper PA-23-150 Apache. During a training flight, the left propeller would not come completely out of feather. When the pilot shut down the engine, the propeller went back into feather regardless of the propeller control position.One of the feather latch weights was broken, probably due to corrosion.Part total time – 1,059 hours.

Piper PA-23-250 Aztec
Wing Tip Failure

The right wing tip fuel tank, installed under STC SA1480WE, separated from the wing during ground operations. The fiberglass around each of the fastener holes that attach the tank to the wing was broken. It appeared the fasteners were properly tightened. In-flight separation of one or both wing tips could cause loss of aircraft control.

Piper PA-28-140 Cherokee
Defective New Part

While complying with the requirements of AD 70-26-04 R2, a technician found the stabilator counterbalance arm tube was defective.The technician ordered a new part from Piper, but it was found to have an extraneous hole in the tube. The hole was positioned at 90-degrees to the normal fastener hole and appeared to be filled with slag. Also, slag was present on the interior of the tube. The extra hole was located at a critical high stress point on the tube, and it was rejected as structurally unairworthy. As received, the hole had been filled with an unknown material and the part painted with a thick coat of zinc chromate and black paint. Part total time – 0 hours.

Piper PA-32R-301 Saratoga
Electrical System Defect

The pilot turned on the landing light during a landing approach, smelled a burning odor and saw smoke. He turned off the master switch and completed the landing safely.The contacts inside the landing light switch housing were worn and dirty, which caused high resistance in the circuit that melted the switch case.

Piper PA-34-200 Seneca
Landing Gear Failure

The pilot could not get the right main landing gear to extend and the aircraft landed with only the nose and left main gear extended.The right main gear was found lodged in the wheel well. The torque links were separated at the center pivot, which prevented gear extension. The torque link bolt was sheared at the center pivot point. There was no evidence of lubrication.Part total time – 1,330 hours.

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