On December 7, 2011 a Sundance Helicopters, Inc., Eurocopter AS350-B2 helicopter, N37SH, operating as a "Twilight tour" sightseeing trip, crashed in mountainous terrain about 14 miles east of Las Vegas, Nevada. The pilot and four passengers were killed, and the helicopter was destroyed by impact forces and postimpact fire. The helicopter was registered to and operated by Sundance as a scheduled air tour flight under the provisions of 14 Code of Federal Regulations (CFR) Part 135. Visual meteorological conditions with good visibility and dusk light prevailed at the time of the accident, and the flight operated under visual flight rules. The helicopter originated from Las Vegas McCarran International Airport, Las Vegas, Nevada, about 1621 with an intended route of flight to the Hoover Dam area and return to the airport. The helicopter was not equipped, and was not required to be equipped, with any on-board recording devices.
The accident occurred when the helicopter unexpectedly climbed about 600 feet, turned about 90 degrees to the left, and then descended about 800 feet, entered a left turn, and descended at a rate of at least 2,500 feet per minute to impact. During examination of the wreckage, the main rotor fore/aft servo, one of the three hydraulic servos that provide inputs to the main rotor, was found with its flight control input rod not connected. The bolt, washer, self-locking nut, and split pin (sometimes referred to as a "cotter pin" or "cotter key") that normally secure the input rod to the main rotor fore/aft servo were not found. The investigation revealed that the hardware was improperly secured during maintenance that had been conducted the day before the accident.
The nut became loose and, without the split pin, the nut separated from the bolt, the bolt disconnected, and the input rod separated from the linkage while the helicopter was in flight, at which point the helicopter became uncontrollable and crashed.
We determined that the probable cause of this accident was Sundance Helicopters’ inadequate maintenance of the helicopter, including:
- the improper reuse of a degraded self-locking nut, (2) the improper or lack of installation of a split pin, and (3) inadequate postmaintenance inspections, which resulted in the in-flight separation of the servo control input rod from the fore/aft servo and rendered the helicopter uncontrollable.
- Contributing to the improper or lack of installation of the split pin was the mechanic’s fatigue and the lack of clearly delineated maintenance task steps to follow.
- Contributing to the inadequate postmaintenance inspection was the inspector’s fatigue and the lack of clearly delineated inspection steps to follow.
As a result of this investigation, we made safety recommendations to the FAA, reiterated a previous recommendation to the FAA, and reclassified a previous recommendation to the FAA.
