NTSB Identification: FTW02LA088.
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Scheduled 14 CFR (D.B.A. American Airlines)
Accident occurred Wednesday, March 06, 2002 in Dallas, TX
Probable Cause Approval Date: 06/30/2004
Aircraft: Fokker F-28 MK-100, registration: N1425A
Injuries: 34 Uninjured.

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 F-100 commercial passenger airplane experienced an uncontained rupture of the auxiliary power unit's (APU) turbine wheel while standing during de-icing procedures. Approximately ten minutes after de-icing began, the Captain reported that he heard and felt a "thud-like" noise from outside the aircraft. At the same time, the APU shutdown. One of the de-icing crewmembers on the ground stated he saw a flame come from the APU exhaust and had activated the ground APU fire bottle discharge switch. Examination of the APU revealed two large holes in the APU's compressor case in line with the turbine wheel's plane of rotation. The turbine wheel was broken into several pieces. A fragment of the turbine wheel was found embedded into a first aid kit that was mounted inside the cabin on the aft wall directly in front of the aft pressure bulkhead. Metallurgical examination of the fractured pieces of the turbine wheel were confirmed that the APU had experienced an overspeed. Further examination did not reveal evidence of fatigue on any of the fracture surfaces. The APU's electronic control unit (ECU) was removed from the engine to interrogate the ECU's non-volatile memory (NVM) and perform a diagnostic test. The NVM indicated that the APU had experienced an overspeed, which is a rotor speed of 107 percent or greater, and had commanded a shutdown. The diagnostic test showed that there were no discrepancies with the ECU. The Automated Surface Observing Station for DFW at 0700 reported winds from 320 degrees at 20 knots gusting to 27 knots. The members of the de-icing crew stated that at the time they were de-icing the airplane, the wind was blowing at 20 knots and gusting. Due to the windy conditions, the drivers of the de-icing trucks had coordinated prior to de-icing the airplane to start at opposite ends of the airplane so the bucket operators would not be spraying each other as they de-iced the airplane. According to company records, all 5 members of the de-icing crew were trained and experienced, and were aware not to spray de-ice fluid in the area of the F-100's APU inlet.

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

The ground crew inadvertent application of deicing fluid in the auxiliary power unit resulting in an overspeed and turbine wheel burst. A contributing factor was the gusty wind.

Full narrative available

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