On June 30, 2007, an Air Tractor AT-502A (registration N6176L) operated by Thiel Air Care, Inc. was involved in an aviation accident near Chowchilla, CA. Investigators recorded the probable cause as: Fatigue fracture and separation of two compressor turbine blades leading to engine failure. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive; 1 related events involving the same aircraft type or operator are linked below.
An aircraft experienced a loss of engine power 20-30 feet above ground during takeoff initial climb, leading to an emergency landing in a pasture. Post-accident examination revealed fatigue fractures in two compressor turbine blades.
Incident Overview
During the takeoff initial climb, the engine lost power at an altitude of approximately 20 to 30 feet above ground level. The pilot subsequently executed an emergency landing in a pasture. The aircraft came to rest upright after colliding with several fences.
Post-Accident Examination
A post-accident examination of the engine determined that the engine failure resulted from the fatigue fracture and separation of two compressor turbine blades. Once liberated, these two blades impacted the remaining compressor turbine blades, causing the airfoil portions of those blades to fracture due to overstress.
Fatigue Crack Analysis
Examination of the fractured blades revealed that the fatigue crack in one blade occupied approximately 40 percent of the fracture surface, while the fatigue crack in the second blade occupied about 60 percent of the fracture surface.
Probable cause
Fatigue fracture and separation of two compressor turbine blades leading to engine failure.