Cessna 207 N917AC

Summary

On 18 May 2001 at about 05:00 local time, a Cessna 207 registered N917AC was involved in an incident near Quinhagak, Alaska, United States. 2 people were on board and nobody was injured. The aircraft was slightly damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

18 May 2001 at 05:00

Classification

Incident

Location

Quinhagak, Alaska, United States

Coordinates

59.6833, -161.8833

Aircraft

Cessna 207

Registration

N917AC

Category

Airplane

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Positioning

Phase of flight

Not recorded

Route

Platinum → Bethel

Aircraft damage

Minor

Weather

VMC

Light

Day

NTSB number

ANC01IA058

Nobody was injured.

An in-flight fracture of the engine crankshaft during descent, precipitated by restricted oil flow through an internal engine oil passage/port.

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

Read the full NTSB narrative

The certificated commercial pilot reported that during a flight earlier on the day of the incident, he had difficulty controlling the propeller rpm, so he elected to make a precautionary landing. The pilot related that after a mechanic replaced the propeller governor, the airplane's engine and governor appeared to be operating normally, so they began their flight back to the operator's base. He said that about 10 minutes after departure, while in cruise, level flight, he noted a light sheen of oil forming on the windshield, and he elected to make a precautionary landing on a remote beach. As he retarded the throttle to start the descent, the propeller rpm increased for about 20 seconds, followed by the propeller detaching from the engine. He said that he was able to glide the airplane to the beach, and land without further incident. The airplane was equipped with a Teledyne Continental Motors (TCM) IO-520-F engine. The propeller and engine crankshaft flange were eventually recovered, and sent to the NTSB metallurgical laboratory for examination. A Safety Board metallurgist examined the fractured crankshaft flange, and reported that his initial visual examination revealed a fatigue fracture, originating from a heat check site. A postincident investigation revealed that the engine crankshaft had been replaced by TCM, 94.3 hours before the crankshaft separation. An engine log book notation, entered by TCM, indicated that the reason for removal was: "...for compliance with CSB 99-3A." According to a representative from TCM's in-house analytical laboratory the crankshaft was a remanufactured part that reportedly was ground undersize, and re-nitrided at TCM. In the presence of an NTSB Investigator, the engine was disassembled. The investigator noted a significant amount of heat discoloration, with modest circumferential scoring of two forward most bearings, just aft of the fractured propeller shaft, indicating a localized loss of lubrication. He added that the oil transfer collar assembly was fractured in one location.

Quoted verbatim from the NTSB record.