Primary finding
Probable cause
a fatigue failure of a compressor blade which resulted in a catostrophic engine failure.
Investigator assessment
Analysis narrative
The pilot reported that immediately after takeoff a total loss of engine power occurred and the airplane pitched nose down. The airplane contacted the terrain off the left side of the runway. The airplane was loaded with 340 gallons of a prowl herbicide/water mixture which spilled. Inspection revealed a failure of one compressor blade which occurred due to high cycle fatigue. This blade failure then resulted in further compressor and turbine blade damage in the engine.
Source record
Factual narrative
On May 5, 1994, at 1015 central daylight time, an Airtractor AT- 402, N91966, operated by Dennis E. McGarity, collided with the terrain following a loss of engine power on takeoff from the Sikeston Airport, Sikeston, Missouri. The accident occurred at the initiation of the CFR 14 Part 137 agricultural application flight. Visual meteorological conditions prevailed and no flight plan was filed. The airplane was substantially damaged and the pilot was not injured. The flight was to have originated at the time of the accident. The pilot reported that immediately after lifting off the runway, a total loss of engine power occurred. He stated the airplane "pitched violently nose down" and collided with the terrain off the left side of the runway. The airplane was loaded with 25 gallons of PROWL Herbicide mixed with 315 gallons of water when the accident occurred. A chemical spill did occur. Post accident inspection by Federal Aviation Administration Inspectors revealed there was internal engine damage. The engine, a Pratt & Whitney PT-6A, was removed and taken to Aviall, Inc., for inspection under the observation of FAA Inspectors. During the inspection, it was determined that an internal failure of the engine had occurred. Compressor and power turbine blades were then shipped to Aviall's Metallurgical Laboratory for further inspection. This inspection revealed, "One C.T. blade had fractured through the airfoil in high cycle fatigue. The nature of the origin could not be determined. The remainder of the C.T. blades had fractured in tensile overload." See attached inspection report. -