NTSB Identification: NYC06IA226.
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Nonscheduled 14 CFR
Incident occurred Friday, September 01, 2006 in Matinicus Islnd, ME
Probable Cause Approval Date: 02/28/2008
Aircraft: Cessna 206F, registration: N8411Q
Injuries: 3 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

After engine start, the pilot heard "an abnormal engine mechanical noise." He shut down the engine and requested a mechanic. During a subsequent engine start, the mechanic confirmed the mechanical engine noise, and the engine was again shut down. Hand propping revealed that the engine would sometimes "mechanically jam," and further examination revealed the fracture of two crankshaft gear teeth. Both gear teeth exhibited signatures consistent with overload. Corresponding starter adapter gear teeth, that would have meshed with the crankshaft gear teeth during the startup, were cracked on the loaded side. All evaluated metallurgical requirements were met, including core hardness, surface hardness and case depth. Although a single "kick back" while cranking could cause the failure of components of the cranking system, there was no evidence as to why a kick back may have occurred.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

An engine kick back of undetermined origin during engine start.

Full narrative available

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