Pilot Debrief

PIPER PA-25-235 near Panama City, FL — 2013-03-18

Final reportERA13LA174
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Date
2013-03-18
Location
Panama City, FL, USA
Aircraft
PIPER PA-25-235
Registration
N86AB
Category
Airplane
Highest injury
Minor
Fatalities
0
Phase of flight
Climb

Probable cause

A loss of preload to the crankshaft gear attachment bolt, resulting in rotation of the crankshaft gear and a subsequent total loss of engine power. The root cause for the loss of preload could not be determined during a postaccident examination of the components.

NTSB narrative

The pilot departed and picked up an aerial advertising banner for a local flight. About 6 minutes later, the airplane's engine suddenly lost all power. The pilot unsuccessfully attempted to troubleshoot the loss of engine power, jettisoned the banner at an altitude of about 500 feet, and performed a forced landing to a pine forest below, which resulted in substantial damage to the airplane. Postaccident examination of the engine revealed that the crankshaft gear alignment dowel had sheared and that the gear had rotated from its normal position. The gear's attaching hardware remained installed and undamaged. Detailed examination of the gear and alignment dowel showed that their hardness was consistent with that required by the design and that they were within or nearly within nominal dimensional tolerances described by the manufacturer. The counter-bored pilot hole at the aft of the crankshaft where the gear was seated was between 0.0008 and 0.0013-inch oversized. There were no discrepancies found with the retaining bolt, and it could be threaded into the crankshaft with minimal resistance. A definitive cause for the loss of preload to the crankshaft gear attaching bolt could not be determined during the engine examination. Review of maintenance records showed that the engine had been installed onto the accident airplane following an overhaul, which was originally precipitated by a propeller strike. The records provided that documented the overhaul and returned the airplane/engine to service lacked language specifying compliance with a manufacturer service bulletin that provided explicit instructions for the installation of the crankshaft gear to the crankshaft; however, the provided records did document part numbers and torque values consistent with those specified by the service bulletin.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Proper assembly and inspection of the crankshaft gear during overhaul could have prevented failure.

NTSB coding

Evidence available

  • Photos
  • 8 docket documents
View NTSB final reportView NTSB docket

Docket documents8

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