DULLES, VA, USA
N488UE
British Aerospace JETSTREAM 3201
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.
HISTORY OF FLIGHT On October 20, 2000, at 1700 Eastern Daylight Time, a British Aerospace Jetstream 3201, N488UE, operated by Atlantic Coast Airlines (ACA) d/b/a United Express flight 7518, was substantially damaged from an uncontained failure of the right engine during descent to Washington Dulles International Airport (IAD), Dulles, Virginia. The 2 certificated airline transport pilots and 11 passengers were not injured. An instrument flight rules (IFR) flight plan was filed for the flight between Patrick Henry Airport (PHF), Newport News, Virginia, and IAD. Visual meteorological conditions prevailed for the flight conducted under 14 CFR Part 121. According to the crew, the airplane was level at 8,000 feet when they were cleared by air traffic control (ATC) to 5,000 feet. A descent was initiated by reducing power on both engines, and the estimated torque was between 20-30 percent. As the flight descended through approximately 6,500-6,000 feet, at an airspeed of approximately 200 knots, the crew heard a loud bang. They then felt a vibration and observed a right "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 and discharged the first fire bottle into that engine, and the "FIRE" warning light extinguished. The crew declared an emergency, secured the right engine, and landed uneventfully at IAD on Runway 1R. PERSONNEL INFORMATION The captain held an airline transport pilot certificate with ratings for multi-engine land, and instrument airplane. He also held a flight instructor certificate for airplane single engine and multi engine land, and instrument airplane. He was type-rated in the BA-3100. He reported a total of 3,610 hours, of which 1,209 hours were in make and model. His most recent Federal Aviation Administration (FAA) first class medical was issued on September 19, 2000. The first officer held an airline transport pilot certificate with ratings for multi-engine land, and instrument airplane. He also held a flight instructor certificate for airplane single engine and multi engine land, and instrument airplane. He was type-rated in the BA-3100. He reported a total of 3,009 hours, of which 149 were in make and model. His most recent FAA first class medical was issued on September 29, 2000. The first officer was the pilot flying, and was seated in the front left seat of the airplane. During the flight, he was receiving his initial operating experience (IOE) for captain upgrade. AIRCRAFT INFORMATION Examination of ACA maintenance records revealed that the engine was removed from the No. 1 position on March 27, 2000, for low oil pressure at idle. The engine was shipped to Garrett Aviation Services, Augusta, Georgia, for repair. Garrett Aviation Services accomplished a continuing airworthiness maintenance (CAM) inspection on the engine at 18,915.1 total hours since new, and 21,593 cycles since new on May 18, 2000. According to ACA, the CAM inspection was accomplished in accordance with Service Bulletin (SB) TPE331-72-0476, Revision 24. During the inspection, a new bull gear was installed into the gearbox in accordance with Alert Service Bulletin TPE331 A72-2062. Additionally, the gearbox diaphragm housing assembly was removed from the gearbox because of a worn high-speed pinion gear oil jet port. The diaphragm was shipped to Honeywell's Repair and Overhaul facility, Phoenix, Arizona, on April 18, 2000. The diaphragm was inspected and returned to Garrett, Augusta, and reinstalled on the engine. The records also indicated that the other oil jets on the diaphragm were replaced during this inspection. The engine was installed on June 20, 2000, at 18,915.1 hours since new and 21,593 cycles since new. According to ACA engine maintenance records, the engine had accumulated 19,512.1 hours since new, 22,369 cycles since new, and 597.0 hours and 776 cycles since the last CAM inspection. FLIGHT RECORDERS A B&D cockpit voice recorder (CVR) was brought to the Safety Board audio laboratory on October 23, 2000. A CVR group convened on November 1, 2000, and produced a transcript consisting of 17:13 minutes of the 30:24 minute recording. A flight data recorder (FDR) was not installed. WRECKAGE DESCRIPTION The Safety Board, along with ACA and Honeywell, performed an examination of the airplane and engine on October 20-21, 2000, at the ACA hangar at IAD. At this time, a Powerplants Group was convened. The examination 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 10 3/4-inches above seat 1A's seat cushion, and 8-inches forward of the seat back cushion. The right side interior wall penetration measured 4 1/2-inches long by 2 3/4-inches wide just above seat 1C's seat cushion, and 1 3/4-inches forward of the seatback cushion. The right side exterior of the fuselage had three holes. There was a 4-inch long by 1 1/2-inch wide hole that was at an approximate 45 degree angle and was 10 1/2-inches below and in line with the forward edge of the window frame for row 1, seats B and C. There was a 1/2-inch long by 1/4-inch wide hole, 9 1/2-inches below and 1 1/4-inches forward of the window frame for row 2, seats B and C. There was a pinhole 8 1/2-inches below the window frame for row 1, seats B and C. The fuselage and wing root fairing had numerous impact dents below the windows between row 1, seats B and C, and row 3, seats B and C. Windows in row 1, seats B and C, and row 2, seats B and C, each had an impact mark. The right engine was secure to the engine mounts. The exterior of the engine had sooting on the right side and bottom. The engine's exterior cases displayed no penetrations or ruptures. The wires on both sides of the engine were burned and melted. The fuel line at the top of the engine was broken. The lower right chin cowl had a 3-inch long circumferential by 1-inch wide axial section of skin directly aft of the vent at the 8 o'clock position bent outwards slightly. The lower right forward cowl had a 1/8- by 1/8-inch hole 3-inches above the horizontal split line, 5 1/8-inches forward of the rear edge. The paint on the inboard and outboard right engine cowls was blistered. The louvers at the top of the inboard and outboard right engine cowls were burned away. The gearbox had four holes in line with the bullgear. There was a 2 1/2-inch by 2 1/2-inch hole at the 3 o'clock position just aft of the negative torque sensor and above the data plate. There was a 5-inch long circumferential by 1 1/2-inch wide axial hole in the gearbox in the inlet at the 2 to 3 o'clock position. There was a 2 1/2-inch long circumferential by 1 1/2-inch wide axial hole in the gearbox above the torque temperature limiter that had a section of bullgear protruding from the hole. There was a 3-inch long circumferential by 4 1/4-inch wide axial hole in the inlet at the 10 o'clock position. Additionally, there was an axial split in the gearbox at the inlet at the 12 o'clock position, and the gearbox diaphragm was split at the 11:30 o'clock position. The compressor impeller vanes were all in place, but all exhibited deep gouges and circumferential scoring on the leading edges. Several of the impeller vanes were bent opposite of the direction of rotation. The third stage turbine blades were intact and exhibited a white coating at the tips of the airfoil surface. The right propeller was in the feathered position and rotated with difficulty. The number 1 propeller blade had a 3/4-inch wide axial by 1-inch long radial dent on the trailing edge 8 1/2-inches out from the blade butt on the concave side. The engine was removed from the airplane on October 21, 2000, and shipped to the Honeywell Repair and Overhaul Bond Room, Phoenix, Arizona, for disassembly and examination. TESTS AND RESEARCH The gearbox was disassembled and examined at Honeywell's Repair and Overhaul Engineering facility, Phoenix, Arizona, on October 25, 2000, under the supervision of the Powerplants Group. Examination of the gearbox revealed that the bull gear was broken into at least six pieces, five of which were recovered. 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. The Honeywell Engines and Systems materials laboratory, Phoenix, Arizona, accomplished metallurgical examination of the bull gear. The examination 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. ADDITIONAL INFORMATION As a result of this investigation, the FAA was considering an airworthiness directive (AD) 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 CVR was returned to the operator on November 3, 2000. The engine and related components were released to the operator on October 27, 2000.
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
Source: NTSB Aviation Accident Database
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