NTSB Identification: MIA97LA012.
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Accident occurred Monday, October 21, 1996 in SYLVESTER, GA
Probable Cause Approval Date: 02/02/1998
Aircraft: Air Tractor 400, registration: N73080
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 pilot intentionally operated the engine exceeding the maximum temperature limits during aerial application flights which he was advised against by several different individuals. The pilot stated that during an aerial application flight he first heard a loud sound with a subsequent loss of engine power. He initiated a forced landing in a field and after touchdown with the brakes heavily applied to avoid obstructions ahead, the airplane nosed over. Examination of the engine revealed that 7 of the 58 compressor turbine blades were failed near the midspan or platform. Oxidation was detected at one of the 7 blades and creep and necking was detected at the trailing edge of another of the blades. Additionally, severe burn erosion was noted to the trailing edges of the compressor turbine guide vanes. According to the ASM Metals Handbook, creep is a time dependent strain occurring under stress. Additionally, at elevated temperature, the service life of a metal component subjected to either non-vibratory or vibratory loading is predictably limited.

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

Was the pilots intentional disregard for operating the engine contrary to the flight manuals for intentionally exceeding the maximum engine temperature, resulting in creep failure of one of the compressor turbine blades.

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