NTSB Identification: CHI00IA037.
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Scheduled 14 CFR operation of AIR WISCONSIN (D.B.A. UNITED EXPRESS )
Incident occurred Wednesday, December 01, 1999 in CHICAGO, IL
Probable Cause Approval Date: 07/17/2001
Aircraft: British Aerospace BAE 146-200A, registration: N606AW
Injuries: 1 Minor,48 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
The airplane collided with the terminal building at the O'Hare International Airport. The captain reported he used the procedures in the BAE 146 Pilot Operating Handbook, to transfer fluid between the green and yellow hydraulic systems while the airplane was parked at the gate. He stated he then set the parking brake and checked the hydraulic system pressure. The captain reported they completed the before start, starting engines, and after engine start checklists at which time he signaled to the ramp personnel to remove the chocks. He reported the airplane then started to roll forward. He stated the parking brake was set and all four engines were running. The captain reported he tried the green braking and emergency yellow brake systems, however, the airplane continued to move. He then selected the anti-skid switch to battery and positioned the thrust levers to fuel off. The airplane traveled approximately 50 feet prior to contacting the bottom of the upper level of the terminal and a lower level door at gate B-20C. Postincident inspection of the brakes, hydraulic system, anti-skid system, squat switches, and related electrical system components failed to reveal why the airplane would have moved with the parking brake set. The initiation of the rolling event was not captured on the DFDR. The airplane is designed so that the DFDR does not record when the parking brake is set. On December 10, 1999, the operator issued an Alert Bulletin, prohibiting flight crews from performing hydraulic system fluid transfers. On August 25, 2000, the operator issued another Alert Bulletin, once again allowing flight crews to perform hydraulic system fluid transfers. On September 1, 2000, another Alert Bulletin was issued once again prohibiting flight crews from performing hydraulic system fluid transfers.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: An undetermined failure in the hydraulic system, which resulted in the airplane's entire braking system becoming temporarily inoperative. A factor associated with the incident was the airport terminal building that was contacted by the airplane. Full narrative available
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