NTSB Identification: IAD97IA018.
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Scheduled 14 CFR DELTA AIR LINES, INC.
Incident occurred Thursday, November 07, 1996 in DAYTON, OH
Probable Cause Approval Date: 03/31/1998
Aircraft: McDonnell Douglas MD-11, registration: N814DE
Injuries: 209 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
While en route the flight crew experienced a failure of the pitch trim control system. The crew was unable to change the pitch trim by the yoke mounted trim switches or the center console mounted horizontal stabilizer control handles. The crew stated that when the slats were extended on descent, they were unable to change stabilizer trim. Subsequent examination of the horizontal stabilizer pitch trim system found that there was no lubrication on the screw actuator assemblies and that the fuse pin had sheared in the output drive unit of the horizontal stabilizer drive gearbox. The sheared fuse pin locked the horizontal stabilizer in its last set position, as designed. A review of Assembly Orders at Douglas Aircraft (DAC) found that DAC production personnel and DAC Inspection personnel stamped the assembly orders indicating completion and acceptance of the lubrication. However, the investigation revealed that no lubrication had been applied to the screw actuator nuts.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: Failure of the output drive unit shear pin due to lack of lubrication to the screw actuator assemblies. Contributing to the cause was the aircraft manufacturer's production and inspection personnel failing to lubricate the screw assemblies after initial installation and again after washing. Full narrative available
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