NTSB Identification: DEN07LA138.
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Accident occurred Saturday, August 18, 2007 in Alamosa, CO
Probable Cause Approval Date: 01/31/2008
Aircraft: Air Tractor AT-301, registration: N69WN
Injuries: 1 Minor.

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 airplane was conducting aerial applications of anti-sprouting chemicals when the number one cylinder head separated. The windscreen was covered in oil, obscuring the pilot's view. The pilot dropped his chemical load and performed a forced landing to a dirt road. During the landing, the left wing impacted a sand berm and the airplane nosed over, coming to rest inverted, and resulting in substantial damage. The pilot reported no additional anomalies with the airplane's systems. Examination of the fracture surface revealed fatigue cracking initiated from multiple locations in a root of the head threads and propagated in an arc to the outer surface of the combustion chamber wall.

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

The failure of the number one cylinder due to fatigue. Contributing to the accident was the pilot's diminished visual lookout due to the oil covered windscreen.

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