Posted on 11/12/2001 12:01:32 PM PST by Lessismore
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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, 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. 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. [Emphasis added] Two pieces of the disk, which amounted to about two-thirds of it, and three blade slot posts were recovered. 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.
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A simple monkey wrench left inside an engine air inlet cowling could have done this. F.A.A. will propose monkey wrenches are dangerous weapons and confiscate all monkey wrenches from A&P (airframe and powerplant) mechanics.
As previously discussed, it is possible that the cracks in each of the three HPT stage 1 disks discussed in this letter were the result of surface damage. However, the Safety Board recognizes that there is no clear evidence of surface damage on the area of the US Airways disk from which the crack originated and, therefore, it is also possible that the crack in that disk initiated from an undamaged blade slot bottom. Further, metallurgical examination revealed that in the area immediately adjacent to the fracture origination point, the radius between the slot bottom and the forward and aft faces of the disk conformed to the engineering drawing requirements for that radius, suggesting that the area from which the crack initiated also conformed. This possibility raises concerns that the design of the slot bottom of the GE CF6- 80C2 HPT stage 1 disk may not provide an adequate margin of safety even when the disk is manufactured to specifications. Further, during the Safety Board’s examination of the separated disk from the US Airways airplane, it was found that many of the radii between the slot bottoms and the forward and aft faces of the disk either exceeded or were less than the engineering drawing requirements for this radius.
Appearently, the problem is still under investigation!
http://www.airdisaster.com/special/special-aa191.shtml
This is the NTSB recommendation. I haven't found anything definitive regarding what the FAA did in response.
See http://www.ntsb.gov/speeches/former/hall/jh970912.htm for an interesting talk "Remarks of Jim Hall Chairman, National Transportation Safety Board to the International Society for Air Breathing Engines Chattanooga, Tennessee, September 12, 1997"
Don't know, but the Air Force's KC-10 tanker, really just modified DC-10, uses a version of the same engine, although of course they give it a military designation. I don't think we can afford to ground them right now. (Verified with the guy in the next office, who was a KC-10 crew chief)
My guess would be that if the engine failure cut the front wing spar, the outboard section of wing would fold backwards, upwards, and then separate. It might fold towards the fuselage far enough to hit the tail surfaces as it came off the plane.
An on-board explosion big enough to separate both one wing and the tail should have damaged the fuselage enough that there would be bodies in Jamaica Bay and between the bay and the main fuselage impact point. However, in interviews the crews recovering the tail and other parts from the Bay have said that there are no bodies in the Bay.
So either the tail was struck by wing parts following engine failure, or the tail was struck by wing parts following a small on-board explosion near the right wing root. I'd favor the former explanation at this point.
Usually what they do is just recall the ones that have a lot of hours on them
If memory serves on this, the engine mount cracked when the engine was attached to the plane because the mechanics used an unapproved method of installing the engine. They used a fork lift to raise the engine into place and inadvertantly put too much pressure on the pylon mount, which cracked it.
The mount failed on takeoff, but the engine itself did not explode or disinteigrate.
Regards,
I heard some reporterette asking some high Mucky-Muck about the "third debris field". She seemed so proud to be able to use the new BUZZ TERM in her job. Betcha she asks for a raise!
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