Pilot Debrief

CESSNA 172S near Seattle, WA — 2017-07-31

Final reportWPR17LA176
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Date
2017-07-31
Location
Seattle, WA, USA
Aircraft
CESSNA 172S
Registration
N957TA
Category
Airplane
Highest injury
Minor
Fatalities
0
Phase of flight
Descent

Probable cause

The total loss of engine power due to oil starvation as a result of the loose right magneto, which allowed oil to escape and the engine to seize. Contributing to the accident was inadequate maintenance, which failed to identify the loose magneto bolt.

NTSB narrative

During an instructional flight, the engine started running rough and, shortly after the oil pressure light illuminated, subsequently quit. The pilot elected to ditch the airplane in the water close to the shoreline. An onsite examination of the engine revealed that the top bolt of the right magneto was loose and had backed off, which allowed the magneto to become partially separated, leaving a 3/8-inch gap at the top of the magneto where it mounted to the case, which allowed oil to exit the engine. Metal shavings were observed throughout the engine. A review of the maintenance records indicated that the magnetos were removed and overhauled about 9 months before the accident during a 500-hour inspection, which was 420.5 hours of flight time before the accident. The airplane had accumulated about 22 hours of flight time since its last annual inspection, and the loose magneto bolt should have been able to be identified at that time.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Proper torque of engine bolts during maintenance could have prevented failure.

NTSB coding

Evidence available

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

Docket documents8

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