On September 18, 2003, an Air Tractor AT-502 (registration N1528T) was involved in an aviation accident near Fort Pierce, FL. Investigators recorded the probable cause as: The fatigue fracture of the compressor turbine blades likely resulted from a loss of gap between the blade and platforms as a result of the observed corrosion. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
An aircraft aborted takeoff after a loud explosion, overran the runway and struck trees. Investigation found fatigue fractures in two compressor turbine blades, with corrosion on blade platforms closing required gaps, altering vibration frequency per Pratt & Whitney.
Incident Overview
During takeoff, the pilot heard a loud explosion shortly after lift off and aborted the takeoff. The aircraft overran the runway and collided with trees.
Examination Findings
Post-incident examination of the aircraft revealed that the compressor turbine disk had two blades fractured near the platform. The remaining blades exhibited severe impact damage. Fatigue was observed on the fracture surfaces of the two blades that had fractured near the platform. Corrosion was observed on the side of the compressor turbine blade platforms from these two fractured blades. The corroded platform area contained foreign elements mostly composed of phosphate and lead oxide.
Technical Assessment
The corrosion observed had caused a volume change which closed the required gap between blade platforms. According to Pratt and Whitney personnel, this would have an adverse effect on the blade airfoils by altering the natural vibration frequency of the blades. Pratt and Whitney personnel concluded that the distress of the compressor turbine disk was initiated by the fracture of one blade in fatigue from multiple origins. The fatigue fracture of the compressor turbine blades likely resulted from a loss of gap between the blade and platforms as a result of the observed corrosion.
Probable cause
The fatigue fracture of the compressor turbine blades likely resulted from a loss of gap between the blade and platforms as a result of the observed corrosion.