Stinson 108 N6532M

Summary

On 4 March 2023 at about 17:00 local time, a Stinson 108 registered N6532M was involved in an accident near Lampasas, Texas, United States. One person was on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

4 March 2023 at 17:00

Classification

Accident

Location

Lampasas, Texas, United States

Coordinates

31.0633, -98.1819

Aircraft

Stinson 108

Registration

N6532M

Category

Airplane

Year built

1948

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Plano → San Antonio

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

WPR23LA117

Nobody was injured.

Improper case hardening of the crankshaft timing gear, which resulted in the fatigue failure of the gear and a total loss of engine power.

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

Read the full NTSB narrative

While enroute during a cross-country flight, the engine lost total power and the pilot performed a forced landing to a bridge. During the landing, the airplane contacted a cable placed across the bridge and nosed over, which substantially damaged the rudder. Examination of the engine revealed that three teeth of the crankshaft timing gear had separated, and approximately 60 to 90 percent of the remaining gear teeth had been deformed and flattened, which stopped rotation of the camshaft and resulted in a total loss of power. The liberated teeth exhibited evidence of fatigue cracks and subsequent overstress fractures. The crankshaft timing gear and liberated teeth did not meet the 50 HRC (513 HV) standard for case hardening. No evidence of the engine overheating was found, which eliminated the possibility of an altered case hardening of the crankshaft timing gear via engine heat. A review of maintenance records revealed that the engine had been overhauled about 58 operating hours before the accident and all ferrous metal parts were non-destructive tested (NDT), including the crankshaft timing gear; the testing did not identify surface or subsurface cracks. An annual inspection of the engine was performed about 8.4 flight hours before the accident and revealed no anomalies. The accident crankshaft timing gear was likely the original gear to the engine.

Quoted verbatim from the NTSB record.