The National Transportation Safety Board today issued five recommendations to the FAA stemming from an ongoing investigation of an uncontained engine failure on an airliner in Los Angeles. Two of the recommendations are classified "Urgent" by the Safety Board.
The incident occurred on June 2, 2006, when the high- pressure turbine (HPT) stage 1 disk in the left engine, a General Electric CF6-80A, on an American Airlines B-767, failed during a maintenance ground run at Los Angeles International Airport (LAX). Debris from the failed engine punctured the airplane's left and right wing fuel tanks; leaking fuel ignited and damaged the wing and fuselage. Pieces of the ruptured disk also penetrated the fuselage and the right engine, and another, found about 2,500 feet from the airplane against an airport perimeter fence, had crossed two active runways and taxiways. The three maintenance personnel working on board as well as another on the ground were not injured.
"We were fortunate that there were no fatalities or injuries in this serious incident," said NTSB Chairman Mark V. Rosenker. "We need to take every precaution and move rapidly to avoid something similar happening again."
Post-incident metallurgical examination revealed that the disk rupture was the result of a rim-to-bore radial fracture that originated at a small dent found at the bottom of a blade slot. The examination also revealed two other similar cracks on the disk. The disk had accumulated 9,186 cycles in service (48,429 hours), with 5,814 cycles remaining for the disk's life limit of 15,000 cycles.
The Board is aware that, as a result of the LAX incident, the FAA has issued an airworthiness directive with a schedule for maintenance -- removal, inspection, and reworking -- of CF6-80 series HPT stage 1 disks beginning at 6,900 cycles.
The Safety Board, however, is proposing on an urgent basis that the FAA require that the disks be immediately removed for maintenance if they have been in service for more than 3,000 cycles since new or since the last inspection. This significantly more stringent standard would not permit disks to remain in service without inspection beyond the earliest known number of cycles at which cracks have been detected or failure has occurred.