Squawk Box

January 2017 Issue




Drive Shafts

The following information is derived from the FAA’s Service Difficulty Reports and Aviation Maintenance Alerts.

Sheared Pressure Pump Drive Shafts

Beechcraft Model 58 Baron

During a VFR instrument training flight, the instructor noted there was no instrument pressure from either engine. Inspection revealed both engine-driven pressure pumps had sheared their drive shafts. Technicians could not find any obvious reason for both shafts to fail.

Part total time: 88.6 hours

Turbocharger Failure

Columbia LC41-550FG Corvalis

The aircraft was climbing through FL190 when the pilot reported a loss of power. An emergency descent and unscheduled landing followed. As the airplane reached a lower altitude, some power was restored. On landing, inspection revealed that the shaft between the compressor and exhaust wheels had broken into two pieces, disabling the turbocharger.

Part total time: 243.0 hours

Sheared Alternator Drive Shaft

Columbia LC41-550FG Corvalis

Pilot reported loss of the right alternator on final approach to the airport. During taxi operations to the ramp, the pilot reported hearing a noise from the front of the aircraft. Removing the alternator from the engine revealed the alternator drive shaft had sheared off flush with the case located aft of the drive coupling.

Part total time: Unknown

aircraft drive shaft

Worn Magneto Drive Shaft

Partenavia P68C TC

Pre-takeoff magneto check detected no rpm drop when the left engine’s left magneto turned off. Inspection revealed left magneto’s plastic gear shaft was worn, allowing internal gear to vibrate in forward and aft directions. Magneto replaced.

Part total time: 211.0 hours

Cracked Bendix Drive Teeth

Piper PA-28-181 Archer II/III

On attempting to start the engine for a post-maintenance ground run, the propeller turned through approximately three blades then stopped. Propeller was difficult to rotate forward or backward. Inspection of the starter’s Bendix drive shaft revealed cracks in the gear running parallel to the teeth, causing the gear not to properly mesh with the flywheel.

Part total time: 382.0 hours

Set Screw Threads Not Engaged

Piper PA-32R-301T Turbo Saratoga

Aircraft landed with no oil pressure and totally covered in oil. Inspection found the prop governor drive gear idler shaft in lower engine cowl. The stationary idler shaft had been rotating and had worn through the inside of the plug. The set screw holding the idler shaft was in place in the crankcase but appeared to not be engaged with the idler shaft, allowing it to rotate and wear its way through the plug.

Part total time: Unknown