SAN DIEGO, CA, USA
N450AA
Boeing DC-9-82
The crew heard a pop after the nose wheel lifted up during rotation on takeoff and a loss of power occurred on the right engine. An emergency was declared and an uneventful landing was completed. All of the third and fourth stage turbine blades fractured at the root and no fatigue marks were noted. The second stage turbine blades fractured at 1/2 to 2/3 span. All low-pressure turbine nozzle guide vanes exhibited significant leading edge rub and had meshed with adjacent turbine blade trailing edges. The low-pressure compressor drive turbine shaft fractured approximately 25 inches aft of the low-pressure compressor. This fracture was twisted and contained a large area of displaced and galled metal; coke/carbon was observed under the galled metal. The number 3 bearing was damaged; all balls were worn with flat spots up to 1/2 the ball circumference. Spalling was evident on the inner and outer race, but no race spinning was noted. The cage was intact, but worn. No evidence of oil starvation or overheating was evident. A flow check of the oil supply system to the number 3 bearing was completed with no blockage or flow anomalies detected. An inspection by an independent laboratory could not determine a cause for the bearing failure. The number 3 bearing had accumulated 12,487 hours since new.
On June 25, 1999, about 1440 hours Pacific daylight time, American Airlines Flight 2090, a Boeing DC-9-82 (MD-82), N450AA, experienced a contained engine failure during departure from Lindbergh Field, San Diego, California. American Airlines operated the airplane as a scheduled domestic passenger flight to Dallas-Fort Worth, Texas, under the provisions of 14 CFR Part 121. The airline transport pilot licensed captain, first officer, 4 cabin attendants, and 135 passengers were not injured. The airplane was on an instrument flight rules (IFR) flight plan and was not damaged. Visual meteorological conditions prevailed. The flight crew reported that they heard a pop after the nose wheel lifted up during rotation on takeoff. The airplane pulled to the right as they lost power on the right engine. They did not notice any alarms or caution lights. They stated they performed required checklists and secured the engine. An emergency was declared and an uneventful landing was completed at the Miramar Marine Corps Air Station, San Diego. All passengers deplaned normally by the airplane's stairs. A preliminary visual inspection determined that all of the blades were missing from the last stage of the turbine. Damage was also observed on the next stage forward. No damage was apparent to the compressor section. A detailed examination of the engine was performed at American Airlines maintenance facility in Tulsa, Oklahoma, and observed by a Federal Aviation Administration (FAA) inspector. The FAA inspector noted the engine was a Pratt & Whitney JT8D-217C, serial number 725576. He reported that a review of records disclosed that the time on the engine since its installation on this airplane, which coincided with time since its last shop visit, was 3,980 hours. Teardown of the engine revealed that all third and fourth stage turbine blades fractured at the root and no fatigue marks were noted. The second-stage turbine blades fractured at 1/2 to 2/3 span. All low-pressure turbine nozzle guide vanes exhibited leading edge rub and meshed with adjacent turbine blade trailing edges. The turbine case bulged in several areas. The inspector noted the turbine exhaust case and number 6 bearing support exhibited damage consistent with aft movement of the low-pressure turbine. The high-pressure compressor drive shaft exhibited minor damage and all three antirotational pins were present. The low-pressure compressor drive turbine shaft fractured approximately 25 inches aft of the low-pressure compressor end. This was at a point relative to the plane of the 12th stage high-pressure compressor disk and the forward portion of the rear compressor seal tube. This fracture twisted and contained a large area of displaced and galled metal; coke/carbon was observed under the galled metal. The number 4 1/2 bearing oil supply manifold assembly was in good condition with all three oil packings in place and intact. The number three bearing was damaged. All balls were worn with flat spots that were up to 1/2 the ball circumference. Spalling was evident on the inner and outer race, but no race spinning was evident. The cage was intact, but worn. No evidence of oil starvation or overheating was observed. A flow check of the oil supply system to the number three bearing was completed with no blockage or flow anomalies detected. Metallurgical examination by an independent laboratory could not determine a cause for the bearing failure. The FAA inspector noted that the number three bearing had accumulated 12,487 hours and the low-pressure compressor drive shaft accumulated 27,230 hours since new. An American Airlines representative reported that compressor washes were not specified in the maintenance manual for this engine series. A representative for the engine manufacturer noted that the coke/carbon buildup was not in the gas path, therefore, compressor washes would not remove this buildup. He opined this buildup was from burning oil that leaked into a hot area after the bearing failure.
failure of the number three bearing. The resulting oil leak from the bearing led to coke/carbon buildup, which resulted in chafing of the turbine's low-pressure compressor drive shaft on the rear compressor seal tube and subsequent fracture of the drive shaft.
Source: NTSB Aviation Accident Database
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