LOCKHEED P2V 5F near Pocatello, ID — 2017-08-06

Probable cause

Maintenance personnel's failure to secure hardware, which resulted in an uncommanded upward deflection of the left elevator and aft movement of the control yoke and inhibited the flight crew from adjusting the airplane's pitch attitude in flight. Contributing to the accident was the lack of maintenance oversight, which should have identified the unsecured hardware before flight.

Contributing factors

Contributing to the accident was the lack of maintenance oversight, which should have identified the unsecured hardware before flight.

NTSB narrative

The company dispatched the accident airplane to a fire as part of an exclusive contract with the United States Forest Service and under the direction of the Bureau of Land Management. During the airplane's climb, the airline transport pilot, who was acting as pilot-in-command, adjusted the trim to reduce nose-down pressure and subsequently observed an uncommanded aft movement of the control yoke and simultaneous increase in the airplane's pitch attitude. The flight crew attempted to regain pitch control by adjusting the trim wheels, but the airplane continued to maintain a pitch-up attitude. Using coordinated inputs, the flight crew was able to land the airplane without incident. A postlanding examination revealed that the variable camber, or varicam, was damaged during the event. This secondary control surface is directly connected to the elevators and provides a primary structural load path for all elevator loads; thus, any damage to the varicam was considered substantial. Postaccident examination revealed that maintenance personnel had failed to secure the drive stop coupling bolts with lockwire and that one of the bolts had backed out of its bolt hole. Because the varicam likely did not display any deformation before takeoff, as it would have been inspected after the previous flight, the bolt likely backed out sometime during the takeoff. When the flight crew adjusted the varicam trim during the initial climb, the absence of this bolt prevented a section of the drive shaft from rotating, allowing only a portion of the varicam to move. This resulted in the deformation of the left side varicam and subsequent upward deflection of the left elevator, which is hinged to the varicam. The resulting feedback in the cockpit was an uncommanded aft movement of the control yoke, which placed the airplane in a pitch-up attitude that could not be corrected by flight control inputs from the cockpit. The mechanic responsible for installing the lockwire was under stress due to family issues at the time of the varicam was last serviced. The company's task cards indicated that the mechanic failed to lockwire the drive stop coupling bolts to the drive stop, despite noting that the work had been completed by stamping the card with his designation. This omission should have been detected by either the facility's lead mechanic or the quality assurance (QA) inspector through the required inspection item (RII) process. However, the lead mechanic seldom oversaw inspections and most likely did not attempt to review this mechanic's work and others' work, as the investigation revealed 7 additional RII oversights. Further, the QA inspector, whose main duty was to review any work that had been stamped RII by the lead mechanic, failed to notice that the critical flight control areas had not been annotated as RIIs. Although the company retrains its RII staff biennially, the QA inspector did not appear to understand his role in the RII process, as he was reported to have given approvals without verifying if the work qualified as an RII. While the mechanic failed to secure the drive stop coupling with lockwire, the lead mechanic and the QA inspector's lack of oversight contributed to the omission that ultimately resulted in the varicam failure.

Analysis

Primary failure mode

Mechanical failure

First missed decision gate

Failure to secure varicam drive stop bolts with safety wire during maintenance.

NTSB coding

• Flight control sys malf/fail · Enroute-climb to cruise
• Maintenance

Evidence available

• Photos
• 6 docket documents

Docket documents6

• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1form
• Release of Aircraft Wreckage, NTSB Form 6120.15form
• NTSB Examination and Company Interview Reportinterview
• Statement of Party Representatives to NTSB Investigationinterview
• Record of Converationsother
• Accident Photographsphotos

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