NTSB Identification: IAD01FA006.
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Scheduled 14 CFR operation of ATLANTIC COAST AIRLINES (D.B.A. UNITED EXPRESS )
Accident occurred Friday, October 20, 2000 in DULLES, VA
Probable Cause Approval Date: 12/18/2001
Aircraft: British Aerospace JETSTREAM 3201, registration: N488UE
Injuries: 12 Uninjured.
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 aircraft accident report.
The airplane was on the arrival to the destination airport, and was cleared to descend from 8,000 feet to 5,000 feet. A descent was initiated by reducing power on both engines. As the airplane descended through 6,500 feet, the crew heard a loud bang, followed by a vibration, and illumination of the right engine 'FIRE' warning light. The right engine RPM dropped to 80 percent and stabilized at that value. The fire bell also sounded. The crew identified the right engine, discharged fire bottle, and the 'FIRE' warning light extinguished. The engine was secured and the airplane landed uneventfully at IAD. Examination of the airplane revealed that the right engine bullgear experienced an uncontained separation in flight. A 4 5/8-inch long section of the bullgear rim penetrated the right side of the fuselage and was recovered from the left side interior cabin wall above seat 1A's seat cushion. Examination of the right engine gearbox revealed that the bull gear was broken into at least six pieces. The gearbox diaphragm's bull gear bearing bore was measured and found to be over the engine manual's allowable wear limit. The engine's maintenance records show that the bull gear was installed new at the last repair, 597 hours and 776 cycles before the event. Metallurgical examination of the bull gear revealed an initial fatigue fracture that originated on the front face of the bull gear outboard of the hub. There were two other fatigue fractures that were on either side of the initial fatigue fracture. The examination also revealed that the bull gear's web thickness and material hardness conformed to the manufacturer's design requirements. As a result of this investigation, the FAA was considering an airworthiness directive that would require a recurring sampling of oil to be analyzed for increased levels of metal that could be indicative to bull and high speed pinion gear wear.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The manufacturer's lack of dimensional inspection and repair requirements for the gearbox forward and aft diaphragm, which caused the bull gear to shift and resulted in an uncontained separation of the bull gear during flight Full narrative available
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