Washington, D.C. 20594
Safety Recommendation
Date: December 12, 2000
In reply refer to: A-00-121 through -124
Honorable Jane F. Garvey
Administrator
Federal Aviation Administration
Washington, D.C. 20591
In this letter, the National Transportation Safety Board recommends that the Federal Aviation Administration (FAA) take action to address safety issues that were identified during its investigation of an uncontained engine failure 1 that occurred at Philadelphia, Pennsylvania, on September 22, 2000, as a result of cracking and rupture of a high pressure turbine (HPT) stage 1 disk 2 in a General Electric (GE) CF6-80C2B2 engine (see figure 1).
Background
On September 22, 2000, a US Airways Boeing 767-2B7(ER) airplane, N654US, equipped with GE CF6-80C2B2 engines, experienced an uncontained failure of the HPT stage 1 disk in the No. 1 engine during a high-power ground run for maintenance at Philadelphia International Airport, Philadelphia, Pennsylvania. Because of a report of an in-flight loss of oil, US Airways mechanics had replaced a seal on the No. 1 engine’s integral drive generator and were performing the high-power engine run to check for any oil leakage. For the maintenance check, the mechanics had taxied the airplane to a remote taxiway on the airport and had performed three runups for which no anomalies were noted.
During the fourth excursion to high power, at around 93 percent N1 rpm, 3 there was a loud explosion followed by a fire under the left wing of the airplane. The mechanics shut down the engines, discharged both fire bottles into the No. 1 engine nacelle, and evacuated the airplane. Although both fire bottles were discharged, the fire continued until it was extinguished by airport fire department personnel. The No. 1 engine and the airplane sustained substantial damage. 4 The three mechanics were not injured.
This incident raises serious safety concerns because, if it had occurred during flight rather than on the ground during maintenance, the airplane might not have been able to maintain safe flight. Examination of the airplane revealed that a portion of the HPT stage 1 disk penetrated the left wing just inboard of the No. 1 engine pylon. Investigators determined that this portion of the disk, which is approximately 140 square inches and 45 pounds, penetrated a dry bay, made a 1-inch-wide vertical cut through the lower half of the forward wing spar, and penetrated a fuel tank before exiting through the top of the wing and passing over the fuselage. Examination of the engine revealed that the disk rupture split the engine in half, leaving the rear of the engine joined to the front only by the fan midshaft. The disk had separated from the shaft and was completely missing from the engine. Two pieces of the disk, which amounted to about two-thirds of it, and three blade slot posts were recovered.
5 Although an extensive search was conducted, the remaining one-third of the ruptured disk (the piece that passed through the wing) was not recovered. Trajectory analysis performed by the Safety Board indicates that it may have landed in the Delaware River, which is adjacent to the airport.