Cessna 150F N8529G

Summary

On 28 September 2015 at about 20:20 local time, a Cessna 150F registered N8529G was involved in an accident near Port Townsend, Washington, United States. 2 people were on board and 2 were seriously injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

28 September 2015 at 20:20

Classification

Accident

Location

Port Townsend, Washington, United States

Nearest airport

Jefferson County International (0S9)

Coordinates

48.0653, -122.8406

Aircraft

Cessna 150F

Registration

N8529G

Category

Airplane

Year built

1965

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Port Townsend → Burlington

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

WPR15FA268

2 people were seriously injured.

The loss of engine power due to the mechanic's inadequate tightening of the crankshaft gear retaining bolts during an engine overhaul, which resulted in fatigue failure of the bolts and the crankshaft gear dowel pin that allowed the crankshaft gear to separate from the crankshaft.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The airplane, flown by a commercial pilot, had just departed for a local flight when witnesses observed it overhead and heard its engine sputtering and backfiring. One witness reported that he thought he heard the engine stop completely. Another witness reported seeing the airplane go out of sight behind a stand of trees and then hearing the sound of a crash. Postaccident disassembly and examination of the engine revealed that all four crankshaft gear retaining bolts had failed in their threaded portions, which had resulted in separation of the crankshaft gear from the crankshaft. Two of the crankshaft gear retaining bolts exhibited gross plastic deformation in their shank portions, and both of these bolts exhibited fractures consistent with overstress. The other two bolts did not exhibit gross plastic deformation, and both of these bolts exhibited flat fractures and crack arrest marks consistent with fatigue fractures. Further, the crankshaft gear dowel pin was fractured, and examination of the pin revealed that it had failed due to fatigue, which could only occur if the crankshaft gear bolts were loose during engine operation. The total time on the engine since its most recent overhaul was 41.4 hours. Although the mechanic who performed the overhaul stated that he had used a calibrated torque wrench to properly torque the bolts during the overhaul process, the loose condition of the crankshaft gear retaining bolts was most likely due to the bolts not being correctly tightened during the overhaul.  

Quoted verbatim from the NTSB record.