Final Report: Maintenance Flaws Led to Fatal Helicopter Crash

 - October 2, 2009, 11:20 AM

Eurocopter AS 350BA, Princeville, Hawaii, March 8, 2007–The NTSB has blamed the fatal crash on the failure of maintenance personnel to properly tighten the flight control servo lower attachment clevis and reinstall a functioning lock washer, which resulted in a flight control disconnect and complete loss of control. Contributing to the accident was the operator’s failure to ensure its maintenance program was being executed in accordance with federal regulations.

The helicopter was returning from a 45-minute tour when the pilot reported he was having “hydraulic problems.” According to a witness, the helicopter slowed over the Princeville airport runway at an altitude of less than 10 feet before its nose dropped and it crashed.

The ATP-rated pilot and three passengers were killed, and three other passengers suffered serious injuries. The helicopter was substantially damaged in the accident.
Examination revealed that the jam nut, lock washer and safety wire were still attached to their threads on the lower clevis on the left lateral servo and rotated freely. The lock washer was worn and missing its locking tang. Further testing of the unit found that a lack of torque of the servo attachment nut along with a worn lock washer would allow the servo to rotate off the clevis.

FAA-issued operations specifications allowed the tour company to maintain its helicopters as prescribed by the original OEM specifications. A review of the accident helicopter’s maintenance log showed that the left lateral servo had been removed and replaced the previous month but there was no required inspection item stamp from an additional reviewing mechanic as specified by the company’s general operating manual.

During the investigation, maintenance discrepancies were noted at the company’s facility, including failure to comply with OEM-mandated work cards, and a disregard for company policy of using the latest version of the OEM maintenance CD. The most recent CD found on the premises was three revisions out of date. During interviews with investigators, the mechanics cited an improper torque value prescribed in a service bulletin for the upper clevis, which was lower than the value the maintenance manual prescribed for the lower clevis.