Pilot Debrief

DWYER MICHAEL D Q near Spring Hill, FL — 2022-03-17

Final reportERA22LA159
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Date
2022-03-17
Location
Spring Hill, FL, USA
Airport
BKV
Aircraft
DWYER MICHAEL D Q
Registration
N3QP
Category
Airplane
Highest injury
None
Fatalities
0
Phase of flight
Climb

Probable cause

The pilot’s improper modification of the pull starter motor, which resulted in its failure and the subsequent loss of engine power.

NTSB narrative

The pilot was also the owner and builder of the experimental amateur-built airplane. While returning to the airport after a local flight, the engine lost oil pressure, so the pilot diverted toward the nearest airport. The engine then began to run roughly and lost partial power. The airplane was not able to glide to the runway and collided with a ditch in a field during the forced landing. The pilot described that his postaccident examination of the engine revealed that the pinion gear on the pull starter motor fractured into several pieces that entered the accessory gear case, likely seizing the oil pump. About 4 years and 100 flight hours before the accident, the pilot had modified the pull starter motor from its original design so that the motor would fit in the airplane. Postaccident metallurgical examination found that the pull starter motor’s pivot lever was shortened. The pivot lever arm was designed to move the starter clutch and engage the pinion (small) gear to the crankshaft gear. The pinion gear teeth displayed indentations in their surfaces that indicated that they were only partially engaged to the crankshaft gear when the starter was being operated, a condition which was likely the result of the shortened pivot lever. This ultimately resulted in increased stress on the gear teeth during engine start and the subsequent failure of the gear in overstress. The liberated gear teeth likely damaged and seized the engine oil pump, and resulted in the partial loss of engine power.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Pilot could have conducted maintenance checks before the flight.

NTSB coding

Evidence available

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

Docket documents5

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