Aviation investigators said Monday they have found a pre-existing fatigue crack in the shattered fan hub of an engine that exploded on a Delta Air Lines plane before takeoff from Florida, killing a Michigan woman and her 12-year-old son.
"A crack of this nature certainly would be something that could generate this hub failure," said George Black, a member of the National Transportation Safety Board, which is investigating the crash. "It's certainly a very good lead."The runway accident Saturday at Pensacola Regional Airport killed a Michigan mother and her 12-year-old son as Delta Flight 1288 was speeding down the runway for takeoff. Two other children in the family suffered minor injuries.
The surviving children were being driven home to the western Michigan town of Scottville by their father because they were afraid to fly, a family friend said.
Investigators said the plane's engine was removed from another aircraft in November and work done on it in December before it was reinstalled in January on the Delta McDonnell Douglas MD-88 jetliner whose 100-pound engine rotor cracked in two, apparently triggering the fatal engine blowup.
At a briefing Monday evening, investigators said a preliminary inspection of the two pieces of the failed hub found the crack, which started in a half-inch bolt hole and migrated about an inch. The hub parts were being sent to Washington for further analysis.
Asked if the crack had caused the failure, NTSB investigator Mike Marx said, "It appears to have, yes. A crack of that size probably is sufficient to cause the separation of the disk."
Investigators said the crack could not have been found by a "walk-around" inspection. They said it was too early to tell whether the crack should have been detected. The probe of the accident will include a review of Delta's maintenance programs.
Pratt & Whitney said its JT8D-200 jet engines had never had a fracture of the kind seen in the Pensacola incident. A company spokesman said Pratt & Whitney, a unit of United Technologies Corp., had sold 2,621 of the JT8D-200 engines over the past 16 years.
Black said earlier Monday that investigators were looking into a possible link between the incident that prompted the overhaul and Saturday's explosion.
Delta, which declined to comment on NTSB statements Monday, has said the engine was removed from another plane Dec. 21 after a problem with an oily, smoky smell in the passenger cabin. Maintenance workers found there was a leaking carbon seal that allowed oil from the engine to get into the air conditioning pack and transferred the smell into the air conditioning systems.
Investigators said they had found 31 of 34 fan blades from the wrecked engine. Part of the scarred engine housing or cowling was found on the runway near the plane.
A review of the cockpit voice recorder indicated that one of the plane's crew had discovered oil on the engine before the flight but it had not been considered a serious problem. Investigators said they did not know if it had contributed to the incident.