Pilot Debrief

PIPER PA 46 350P near Tahlequah, OK — 2017-07-30

Final reportCEN17LA292
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Date
2017-07-30
Location
Tahlequah, OK, USA
Airport
TQH
Aircraft
PIPER PA 46 350P
Registration
N786MD
Category
Airplane
Highest injury
Minor
Fatalities
0
Phase of flight
Climb

Probable cause

The total loss of engine power, which resulted from fatigue failure of two engine through bolts and the No. 2 cylinder attachment studs due to the lack of sufficient clamping force.

NTSB narrative

The private pilot reported that he was in cruise flight when the engine experienced a total loss of power. Oil covered the windshield and smoke filled the cockpit, making it difficult for him to see out of the airplane. He attempted to land at an airport but conducted a forced landing to a field about 300 ft short of the runway. The right wing separated from the fuselage when it hit a hay bale. The examination of the engine revealed a large hole in the engine case near the No. 2 cylinder. The engine maintenance records indicated that when the engine had a major overhaul about 8 years before the accident, the engine crankcase was repaired at a facility specializing in crankcase repairs. The facility typically used glass bead media to clean engine crankcases instead of "mildly abrasive organic substances" as required by the engine manufacturer. About 1 year before the accident, about 825 hours since the major overhaul, all 6 cylinders were replaced. The engine failure occurred about 198 hours after the cylinders were replaced. The metallurgical examination of the eight through bolts revealed that two of the through bolts and the No. 2 cylinder studs had fracture surfaces that were consistent with fatigue. The fatigue in the studs and through bolts likely resulted from insufficient clamping force due to insufficient torque applied to the attachment nuts during installation or could have developed in service as asperities on the clamping surfaces worked down over time, leading to a reduction in clamping force.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Pilot could have diverted to TQH sooner after engine power loss began.

NTSB coding

Evidence available

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

Docket documents8

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