COVINGTON, KY, USA
N723DA
Lockheed L-1011-385-1
The flight attendant was in the elevator when it dropped to the galley level, and she received a fractured ankle. The elevator was operated by a drive shaft with two co-located shafts. The inner shaft was located inside the secondary shaft. Examination of the elevator lift mechanism revealed that the primary shaft had failed in rotating-bending fatigue. The secondary shaft failure originated from a fatigue crack in a sharp corner of the teeth. Corrosion was found on the surface of the crack. The shafts were inspected at 300-hour intervals, and had last been inspected 33 hours prior to the accident.
On June 26, 1997, at 2350 eastern daylight time, a fight attendant was seriously injured in a galley elevator while the Lockheed L-1011-385-1, N723DA, operated by Delta Air Lines as flight 1885, was being pushed back from the gate at Covington, Kentucky. There were no injuries to the cockpit crew of 3, the remaining 7 flight attendants, or the 85 passengers onboard the airplane, which was not damaged. Visual meteorological conditions prevailed for the flight destined for Atlanta, Georgia. An instrument flight rules flight plan had been filed for the flight that was conducted under 14 CFR Part 121. According to the Captain's statement: "...As we began pushback, a Flight Attendant called the cockpit and advised that a Flight Attendant had been injured in the right (First Officer's) galley elevator. I stopped the pushback so that I could get more information...[the flight attendant] advised that she had been bruised and that her ankle was swollen. The lift had fallen from passenger level down to galley level...We called the local emergency medical team for assistance...The EMT's transported her to a local hospital...." The investigation revealed that the elevator was operated by an electric motor driving two shafts that were co-located. The primary shaft lay inside of the secondary shaft. The primary shaft carried the load until it failed, at which time two dogs on the secondary shaft engaged the lift sprocket, to raise/lower the galley elevator. A failure of the primary shaft could be detected by visual inspection of a washer at the end of the shaft. According to Engineering Report 7-72422-20, from Delta Air Lines, Inc., dated July 18, 1997: "...In the flight, DAL flight # 1074 from Los Angeles (LAX to CVG) which was immediately prior to the accident flight, the flight attendants had noticed that the galley lifts were not flush with the service center floor. However, this was not considered unusual by the flight attendants and not reported to maintenance. Consequently no special attention was paid to the galley lift system and it was not inspected at the end of flight 1704...." "...The failure mechanism of the primary shaft from the macroscopic appearance of the fracture surfaces...appears to be by rotating-bending fatigue...." The report also stated: "The failure mechanism of the secondary shaft was by fatigue crack growth at the base of the dog teeth. The cracks started out of the sharp corner at the junction of the teeth and the shaft body. There were three regions on the fracture surfaces: an thumbnail shaped fatigue crack initiation area, followed by indistinct but continuous striations, and a final fast fracture region showing ductile overload failure. Corrosion was evident in some areas of the surface indicating that the fatigue crack had been propagating form some time...." The report further stated: "...The free-fall of the lift was caused by failure of the primary shaft and the two dog teeth on the secondary shaft which are parts of the sprocket assembly. The failure of the secondary shaft dog teeth was unexpected as the design of the sprocket assembly included a 'fail-safe' mechanism that would indicate primary shaft failure after which the secondary shaft dog is supposed to carry the torque load for a duration of at least 300 hours, which is the interval between inspections of the fail-safe mechanism...." According to the Delta Air Lines maintenance program, the area was last inspected on a service check, on June 23, 1997, 33 hours prior to the accident.
the failure of the primary and secondary elevator driveshafts, and the failure of maintenance personnel to detect the failure of the primary shaft during scheduled inspections.
Source: NTSB Aviation Accident Database
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