Pilot Debrief

NORTH AMERICAN NAVION near Alamogordo, NM — 2016-06-24

Final reportCEN16LA234
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Date
2016-06-24
Location
Alamogordo, NM, USA
Aircraft
NORTH AMERICAN NAVION
Registration
N91137
Category
Airplane
Highest injury
None
Fatalities
0
Phase of flight
Cruise

Probable cause

The failure of the No. 5 exhaust valve key spring, which resulted in a total loss of engine power.

NTSB narrative

The commercial pilot stated that, while in cruise flight, the engine began to run rough and that he noted that the Nos. 1 and 5 cylinders were indicating significantly cooler temperatures than the other cylinders. About 12 minutes later, the pilot noticed an "acrid metallic smell" in the cabin. The pilot turned the airplane toward the closest airport as the engine continued to run rough and produce a "metallic clanking" sound. Unable to reach the airport, the pilot made a forced landing in a field about 100 yards short of a road. The airplane continued into a drainage culvert and came to rest on the road. A postaccident examination of the engine revealed that the engine crankcase was cracked at the base of the No. 5 cylinder and the cylinder's rocker box cover exhibited multiple holes. The oil sump contained a large amount of metal debris and damaged components from the No. 5 cylinder. The No. 5 cylinder exhaust valve spring key was worn and damaged. The exhaust valve guide was fragmented and the valve guide bore was worn beyond the specified size, which indicated the valve guide was moving inside the guide bore. The No. 5 piston and cylinder damage were a result of the valve being released into the cylinder during engine operation. It is likely that the valve spring key failed and allowed the valve to release into the cylinder.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Pilot could have landed earlier upon noticing engine issues at 0958.

NTSB coding

Evidence available

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

Docket documents9

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