Bolt Confusion

AD on Lycoming crank bolts complicated by supplier part numbers


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


Some operators of aircraft with Lycoming -540 series engines who were hit by a pair of crankshaft bolt ADs last year got another letter from the FAA: Never mind.

The emergency AD and the superceding AD issued in December required owners of Lycomings big six-cylinder engines to replace the crankshaft gear retention bolt. The AD cut across applications, applying to aerobatic engines, turbos, left-turning engines and for airplanes and helicopters. Although it applied only to those engines with a Lycoming part number STD-2209 retaining bolt, many people didnt make that distinction.

The FAA has reiterated that if you can confirm that a different part number bolt is installed or if the bolt came from Lycoming kit 05K19987, the AD does not apply to the engine. Furthermore, its important to determine the part number of the bolt, not merely the supplier, to determine if the AD is applicable.

If the owner can confirm that the bolt was manufactured with a different part number, such as Superior Air Parts part number SL-SDT-2209, then the engine is not affected by the AD.

Complicating the matter is that Superior supplied some bolts to Lycoming with the Lycoming part number. Those bolts are subject to the AD.The Superior bolt is stamped with an SL on the head, while the affected Lycoming bolts are not stamped.

Beech A-36 Bonanza
Nose Landing Gear Failures

During a landing approach, the pilot placed the landing gear control in the down position but the nose gear did not extend. Investigation revealed that the nose gear actuator arm had failed.Part total time – 3,150 hours.

Beech 58 Baron
Broken Compressor Bracket

During an inspection, the technician discovered the mounting lobe was completely broken off the bracket that holds the air-conditioner compressor to the front of the left engine.The bracket is attached to the engine case with four bolts. While installing the new bracket, the technician placed shims under some of the mounting lobes to avoid a preload condition after the bolts are torqued. An improper shimming during installation may have caused the failure.Part total time – 303 hours.

Cessna 172 M and N
Fuel Leak in Cabin

In two different reports, owners complained of fuel smell in the cabin. Upon inspection, technicians found the fuel line couplers under the headliners dry-rotted. The air vent duct work ran on top of the fuel vent line and, over time, became corroded, allowing water to leak onto fuel line.Part time – 1,717 and 2,668 hours.

Cessna 172N Skyhawk
Stabilizer Spar Cracks

During an inspection of the horizontal stabilizer spar, the technician found a crack around the center lightening hole. The spar and reinforcement were both cracked inboard of the stabilizer attachment holes.Part total time – 8,135 hours.

Cessna 180K
Rudder Control Failure

During landing, the CFI was flying the aircraft from the right seat. The aircraft departed the runway to the right, even though the pilot applied full left rudder.An investigation revealed that the left storable rudder pedal unlocked when firm pressure was applied. Further inspection revealed the bellcrank was bent.Part total time – 2,068 hours.

Learjet 25
Fuel Filter Failure

When the pilot powered up the engines, the left low-pressure fuel light came on.The technician discovered the low-pressure fuel filter gaskets that are attached to the filter were not glued evenly on the entire surface. This caused the gasket to act as a restrictor for the outlet fuel. As the engine demand for fuel increased with RPM, the restriction was great enough to drop the fuel pressure to below the pressure switch limit. The right low-pressure filter gasket displayed the same defect.The submitter checked all the fuel filters in his stock, and they all displayed the same defect. He removed the defective fuel filters from his stock and notified the vendor.

Piper PA-28-181 Archer III
Rudder Control; ATA 2720

During a training flight, the pilots right rudder pedal was unresponsive. The pilot landed the aircraft without incident.The technician discovered the pilots right rudder pedal and toe brake assembly were both disconnected from the idler arm and brake cylinder. He found the clevis pin on the cabin floor beside the cotter pin.Part total time – 2,872 hours.

Piper PA-31-350 Chieftain
Main Gear Component Failure

During an approach, the left main landing gear warning light illuminated, which indicated it was not down and locked. Observation by ground personnel indicated the gear appeared to be down, and the airplane landed without incident.The technician discovered a broken wire in the left main landing gear downlock switch.The FAA Service Difficulty Reporting Program database contains 21 reports on the Piper PA-31-350 downlock switch.


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