NTSB Identification: MIA99LA203.
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Accident occurred Friday, July 23, 1999 in DREW, MS
Probable Cause Approval Date: 03/02/2001
Aircraft: Air Tractor 301, registration: N2368R
Injuries: 1 Uninjured.

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

The flight was departing from a 3,000 foot runway with a full load of fertilizer. The airplane became airborne, and according to the pilot, the engine lost power. The pilot was not able to maintain altitude, and the airplane impacted the ground about 2,500 feet from the departure end of the runway. The on scene investigation revealed that the No. 4 cylinder exhaust rocker box cover was fractured and missing, and appeared to not have been caused by impact with the ground. The No. 4 cylinder was removed from the engine and sent to the NTSB Materials Laboratory in Washington, D.C., for examination. The laboratory examination revealed that the No. 4 cylinder head had failed from fatigue cracking, probably the result of both mechanical and thermal stresses. It was likely that the fatigue originated first at the corners of the exhaust rocker shaft hole in boss '1', then initiated at localized casting defects in boss '2' as the fatigue in boss '1' grew and the local stresses increased in the remaining structure.

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

a loss of engine power due to the failure of cylinder No. 4 boss, which was caused by fatigue cracking, resulting in a forced landing in marshy terrain and subsequent nose over.

Full narrative available

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