MIAMI, FL, USA
N66734
Boeing 727-224
During the initial part of the takeoff, prior to the engines reaching takeoff power, the No. 2 engine had an uncontained failure of the 8th stage HPC disk. The takeoff was aborted, the passengers were bussed to the terminal, and the aircraft was towed to the gate. Metallurgical examination of the 8th stage HPC disk showed that a significant amount of cadmium was present on steel base metal in the area of the fracture surfaces and the surface had an inadequate nickel coating. The disk had accumulated 359 flight hours since overhaul. The disk had been nickel-cadmium plated in March 1996 and was stored until February 1998, when it was installed in the accident engine during repair. Other HPC disk installed in the accident engine, which had been nickel-cadmium plated by the same company as the 8th stage HPC disk, were also found to have inadequate nickel coating. During nickel-cadmium plating the nickel acts as a barrier coating between the cadmium and the steel part to prevent cadmium from contacting the steel part, which can cause cadmium embrittlement.
HISTORY OF FLIGHT On October 7, 1998, about 0709 eastern daylight time, a Boeing 727-224, N66734, registered to First Security Bank NA, and operated by Continental Airlines, Inc., as flight 1521, Title 14 CFR Part 121 scheduled domestic passenger service from Miami, Florida, to Houston, Texas, had an uncontained failure of the No. 2 engine during takeoff roll at Miami. Visual meteorological conditions prevailed at the time and an instrument flight rules flight plan was filed. The aircraft received substantial damage. The airline transport-rated captain, first officer, flight engineer, 3 flight attendants, and 75 passengers were not injured. The flight was originating at the time of the accident. The captain stated he was flying the aircraft and advanced the engine power levers for takeoff. The engines spooled up, and just prior to maximum takeoff power being set, he heard a loud bang noise. He retarded the power levers and aborted the takeoff. He turned off the runway at the next taxiway. The No. 2 engine was identified as having failed and the engine shutdown procedure was accomplished and the fire handle was pulled. The fire bottles were then fired. He made contact with the fire department personnel who arrived shortly after the aborted takeoff and they reported there was no fire. A portable airstair was brought to the aircraft and the crew and passengers deplaned and were taken to the terminal building by bus. PERSONNEL INFORMATION Information on the flightcrew is contained in this report under First Pilot Information and in the Pilot/Operator Aircraft Accident Report. AIRCRAFT INFORMATION The No. 2 engine was a Pratt and Whitney model JT8D-9A, serial number 657091. At the time of the accident the engine had accumulated 68,784 total flight hours and 57,530 total cycles. The engine had accumulated 4,846 flight hours since overhaul and 359 flight hours since repair. On March 2, 1998, 359 flight hours before failure, the No. 2 engine was repaired by General Electric Engine Services, Miami, Florida. The N1 and N2 compressors, hot section, N2 turbine and exhaust case were repaired under heavy maintenance criteria. The N1 turbine and main accessory gearbox were repaired under heavy repair criteria. Installed were the C-5, C-6, C-8, C-9, and C-10 disks. The C-8 or 8th stage high pressure compressor (HPC) disk, which was installed at this time, had been overhauled by General Electric Engine Services (formerly Greenwich Air Services), Miami, Florida, on February 11, 1998. Records showed the disk was received by Greenwich Air Services in March 1996. The disk was sent to Action Plating Corporation, Opa-Locka, Florida, for stripping. The disk was then returned to Greenwich Air Services, where it was inspected. The disk was then sent by Greenwich Air Services to Wings Aviation Services, Miami, Florida, for plating with diffused nickel-cadmium. The disk was then stored until February 1998. (Additional aircraft information is contained in this report under Aircraft Information and in the Powerplants Group Chairman Factual Report). METEOROLOGICAL INFORMATION Visual meteorological conditions prevailed at the time of the accident. Additional meteorological information is contained in this report under Weather Information. FLIGHT RECORDERS The cockpit voice recorder from N66734 was not retained by NTSB, for it remained electrically powered after the accident and the event was over written. The digital flight data recorder from N66734 was retained by NTSB after the accident and forwarded to the NTSB Vehicle Reorders Division, Washington, D.C., for readout. The readout showed the aircraft aligned with the takeoff runway and engine power was advanced. The engine pressure ratios increased to 1.44, 1.51, and 1.46, on engines 1, 2, and 3 respectively. The recording on the digital flight data recorder then ends. (See Flight Data Recorder Specialist's Factual Report of Investigation). WRECKAGE AND IMPACT INFORMATION Examination of the aircraft after the accident showed the No. 2 engine had experienced an uncontained failure of the 8th stage HPC disk. The two forward pieces of the No. 2 engine cowling separated and were found on the runway. Damage to the vertical tail had occurred from ejected engine components. Pieces from the 8th stage HPC disk were located inside the vertical tail of the aircraft, about 500 feet to the right of the aircraft, and about 500 feet to the left of the aircraft. (Additional Wreckage and Impact information is contained in the Powerplants Group Chairman Factual Report) MEDICAL AND PATHOLOGICAL INFORMATION There were no reported injuries from the three flightcrew members, 3 flight attendants, and 75 passengers. The flightcrew members did not submit to toxicology testing after the accident. TESTS AND RESEARCH Metallurgical examination of the 8th stage HPC hub fracture surfaces revealed the presence of a crack extending inboard from the rim radius, intersecting a shielding hole, and continuing partially into the bore. Elemental analysis of the fracture surface revealed a significant amount of cadmium in contact with the steel base material. The hub was nickel-cadmium (NiCd) plated during its last overhaul in March-April 1996, by Wings Aviation Services Inc. (Wings) in Miami. The NiCd plating operation requires applying a base layer of nickel followed by a top layer of cadmium and then baking to diffuse the two elements together. The nickel acts as a barrier coating between the cadmium and the base material (steel) to prevent the cadmium from contacting the steel base material, which may cause cadmium embrittlement. The remaining Wings plated HPC disks from the accident engine were metallurgically examined and found to have inadequate Ni coating. The Federal Aviation Administration (FAA) issued an Airworthiness Directive (AD) to require the removal of JT8D and JT3D HPC disk that had been NiCd plated by Wings based on the number of hours in service that the disk had accumulated since being NiCd plated. (See Powerplants Group Chairman Factual Report and NTSB Materials Laboratory Factual Report). ADDITIONAL INFORMATION The aircraft was released by NTSB to Guy Puglia, Senior Manager Propulsion Engineering, Continental Airlines, Inc., on October 10, 1998. The No. 2 engine and accessories, and the digital flight data recorder, which were retained by NTSB, were released by NTSB to Eugene A. Carroll, Director Safety Investigations, Continental Airlines, Inc., on December 16, 1998. Additional parties to the NTSB investigation were: Avi Swartzon Wings Aviation Services, Inc. Miami, Florida William F. Bain Action Plating Corporation Opa-Locka, Florida Mike Careccia Independent Association of Continental Pilots Houston, Texas John Martens General Electric Engines Services Cincinnati, Ohio Additional NTSB personnel assigned to this investigation were: Jean-Pierre Scarfo-Powerplants Group Chairman Jean Bernstein-Metallurgist David Case- Flight Data Recorder Jeffrey Guzzetti-Powerplants George Anderson-Powerplants Debbie Bruce-Powerplants
The catastrophic failure of the 8th stage high pressure compressor disk from cadmium embrittlement as a result of improper adherence to the prescribed plating procedures and requirements by the company that last plated the disk. Contributing to the accident was the failure of the engine repair company to provide adequate surveillance and oversight of the plating company, the engine repair companies use of an unauthorized repair vendor, the plating company, and the engine repair companies failure to inform the aircraft operator that they had used the plating company which was not on the aircraft operators vendor list. Also contributing to the accident was the aircraft operators failure to audit the engine repair company to the level of detail that they would have discovered the engine repair company was using an unauthorized repair vendor.
Source: NTSB Aviation Accident Database
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