NTSB Identification: FTW04GA076.
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Accident occurred Thursday, February 19, 2004 in San Antonio, TX
Probable Cause Approval Date: 12/03/2004
Aircraft: Schweizer 269D, registration: N255TP
Injuries: 2 Minor.
: NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this public aircraft accident report.
The 493-hour pilot reported that approximately 5 minutes after departure, he noticed a "slight change in engine noise." Subsequently, he heard a "bang," followed by an aural engine warning horn, and a loss of engine power. The pilot initiated an autorotation, and during the autorotation, the helicopter impacted power lines, landed hard on a parking lot surface and came to rest upright. A witness located adjacent to the helicopter's flight path reported hearing a "loud backfire" followed by subsequent white smoke coming from the helicopter. Review of the aircraft maintenance records revealed the engine was overhauled approximately 295 hours prior to the accident. During the engine overhaul, the impeller travel (bump clearance) was measured to be approximately .010 inches. During the engine teardown examination, prior to the removal of the compressor rotor from the rear support, the impeller travel (bump clearance) was measured to be approximately 0.021 inches. The third, fifth, and sixth stage vane assemblies were bent in the direction of rotation. Corresponding damage was observed on the trailing edges of the blades on the adjacent forward compressor rotors. Fretting and score marks noted on the compressor assembly components were consistent with axial movement at the compressor assembly resulting in contact between the compressor blades and vanes, and a subsequent compressor stall and loss of engine power.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The loss of engine power due to the axial movement of the compressor rotor blades contacting the compressor vanes resulting in a subsequent compressor stall. A contributing factor was the improper assembly of the compressor section during the engine overhaul by unknown maintenance personnel. Full narrative available
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