Pilot Debrief

PIPER J3C near Salisbury, CT — 2017-08-13

Final reportERA17LA275
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Date
2017-08-13
Location
Salisbury, CT, USA
Aircraft
PIPER J3C
Registration
N98550
Category
Airplane
Highest injury
Minor
Fatalities
0
Phase of flight
Cruise

Probable cause

An improper replacement of the crankshaft by maintenance personnel, which resulted in a failure of the crankshaft gear and total loss of engine power.

NTSB narrative

During cruise flight, the airplane experienced a total loss of engine power, and the flight instructor performed a forced landing into trees. The engine crankshaft was replaced about 4 years and about 317 hours of operation before the accident. Teardown examination of the engine revealed that the crankshaft gear screws were fractured, and the crankshaft gear was separated from the crankshaft. Fretting was observed near two of the four crankshaft screw holes and corresponded to two elongated screw holes on the crankshaft gear. The crankshaft and crankshaft gear did not contain a dowel pin as specified in the most current versions of the manufacturer's illustrated parts catalog and overhaul manual, which were published more than 2 years before the crankshaft replacement. Additionally, the crankshaft gear did not contain a dowel pin hole, which was consistent with a crankshaft gear for an older, different model engine. Both publications contained numerous instructions and references to use a crankshaft gear with a dowel pin hole and to align the gear to the crankshaft with a dowel pin, which would pilot the crankshaft gear on the crankshaft. Thus, it is likely that when the crankshaft was replaced, maintenance personnel did not use the most recent manuals and installed a crankshaft gear for a different engine, which led to the crankshaft gear's failure and the subsequent loss of all engine power.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Proper maintenance of the engine components could have prevented the power loss.

NTSB coding

Evidence available

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

Docket documents7

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