Pilot Debrief

STINSON 108 near West Creek, NJ — 2017-05-17

Final reportERA17LA182
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Date
2017-05-17
Location
West Creek, NJ, USA
Airport
31E
Aircraft
STINSON 108
Registration
N9366K
Category
Airplane
Highest injury
Minor
Fatalities
0
Phase of flight
Climb

Probable cause

A total loss of engine power due to the No. 4 cylinder’s exhaust valve getting stuck and the subsequent fracturing of the valve face stem.

NTSB narrative

The private pilot reported that, while en route on a cross-country flight, the engine began to "shake." The pilot attempted to return to the airport; however, the engine experienced a total loss of power. The pilot subsequently initiated an emergency descent; however, the airplane struck trees and terrain about 1 mile from the approach end of the runway. The crankshaft and remaining cylinders remained intact, and the engine crankshaft rotated smoothly when the propeller was turned by hand. The No. 4 cylinder's exhaust pushrod shroud and exhaust pushrod were both bent. An examination of the engine revealed that the No. 4 cylinder was fracture-separated from the crankcase. The piston, sections of the No. 4 cylinder, and sections of the crankcase were missing. The No. 4 exhaust valve stem was fractured about halfway along its length, and the fracture surface was consistent with reverse bending fatigue crack propagation, which typically results from a stuck valve. The lower half of the stem and face were missing. The No. 4 exhaust valve guide clearance was excessive, and the valve's guide and tip area contained carbon deposits. The cylinder walls contained circular gouges consistent with the exhaust valve face diameter. It is likely that the carbon deposits on the valve stem resulted in the valve getting stuck, which initiated the reverse bending fatigue crack and led to the exhaust valve face stem fracturing and dropping into the cylinder and the subsequent catastrophic engine failure. The engine maintenance records were incomplete and prevented a determination of when the last clearance check of the No. 4 cylinder was performed or when it was last overhauled/replaced.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Performing a thorough engine inspection before the final leg of the flight.

NTSB coding

Evidence available

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

Docket documents10

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