Pilot Debrief

CESSNA U206 near Van Nuys, CA — 2012-11-25

Final reportWPR13LA052
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Date
2012-11-25
Location
Van Nuys, CA, USA
Airport
VNY
Aircraft
CESSNA U206
Registration
N5229U
Category
Airplane
Highest injury
Minor
Fatalities
0
Phase of flight
Cruise

Probable cause

A partial loss of engine power during cruise flight due to fatigue fractures of two crankshaft gear teeth from corrosion pitting, which resulted in an off-airport forced landing and collision with obstacles on the ground.

NTSB narrative

The pilot reported that the airplane was in cruise flight when the engine started backfiring and he smelled burnt oil; the engine subsequently lost partial power. During the forced landing on a soccer field, the airplane sustained substantial damage when it collided with a fence and trees before coming to rest on its left side. Postaccident examination of the engine revealed that the engine crankshaft would not rotate. A borescope inspection revealed that a valve in the No. 2 cylinder was in contact with a piston face. All of the piston heads exhibited semicircular indentations near the location of the valves. Upon disassembly, six gear teeth on the crankshaft gear were found fractured, and all of the teeth on the camshaft gear were found ground off. A metallurgical examination of the separated crankshaft gear teeth revealed that two of the fracture surfaces exhibited fatigue with areas of corrosion pitting and that the other fracture surfaces exhibited evidence of overload.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Pilot could have conducted a precautionary landing before engine failure.

NTSB coding

Evidence available

  • 9 docket documents
View NTSB final reportView NTSB docket

Docket documents9

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