Piaggio P180 N146SL accident near Henderson, Nevada

Probable cause

The failure of maintenance personnel to properly torque the elevator attachment hardware in accordance with the maintenance manual, which led to the detachment of the elevator. Contributing to the accident were maintenance personnel's failure to identify the loose attachment hardware during a scheduled inspection, the flight crew's decision to continue the flight after identifying a flight control problem, and the flight crew's failure to perform an adequate preflight inspection at the intermediate airport.

NTSB analysis

The twin-engine airplane departed 23 minutes behind schedule to pick up passengers at an intermediate airport. During the takeoff roll, the left elevator departed the airplane and was found off the side of the runway 3 days later. The crew arrived at the intermediate airport and quickly boarded the two waiting passengers. They did not perform an adequate preflight inspection and departed about 5 minutes behind schedule. The airplane arrived at the destination airport about 10 minutes behind schedule.

Upon postflight examination by the crew, the left elevator was observed missing from the tail's horizontal stabilizer. An examination of the attachment nuts on the hinges of the right elevator found that they were finger tight. Examination of the hinge fittings on the left elevator and horizontal stabilizer revealed no mechanical damage or deformation to any of the components. Review of airplane maintenance records showed that an airworthiness directive (AD) had been complied with 54 days earlier, which involved both elevators being removed and then reinstalled.

Materials laboratory examination of one of the right elevator attachment hardware bolt-nut combinations revealed that the self-locking nut exhibited run-on torque values well below the acceptable minimum torque. Based on the finger tight condition of the right elevator attachment hardware and the lack of any mechanical damage to the hinge fittings of the left elevator and stabilizer hinge structure, it is likely that all four sets of attachment hardware for both elevators were not properly torqued during the AD maintenance 54 days earlier. Additionally, 26 days before the event, a phase inspection was completed during which the elevator should have been visually inspected and functionally checked. The airplane had flown 158.9 hours with loose elevator attachment hardware before the two sets of bolts on the left elevator had completely worked their way out of the hinges, and the elevator departed the airplane.

The cockpit voice recorder revealed that the flight crew had experienced unusual pitch control responses during each of the departures and landings. The flight crew could have identified the missing elevator during a preflight inspection at the intermediate airport, yet they decided to continue the flight despite the pitch control problems experienced during the takeoffs and landing.

Text from the NTSB. Open the NTSB docket for WPR12FA332 for the full record.