According to the United States National Transportation Safety Board (NTSB), fatigue-related maintenance error was the probable cause of a Sundance Helicopters crash that killed five people in 2011.
In a meeting webcast live on Jan. 29, the NTSB determined that disconnection of the fore-aft servo control rod — most likely due to a missing safety pin and the improper reuse of a degraded self-locking nut — caused the crash of a Eurocopter AS350 B2 near Henderson, Nev. on Dec. 7, 2011. The NTSB also determined that the mechanic and inspector who performed maintenance on the helicopter shortly before the accident were suffering from fatigue at the time, making fatigue a contributing factor to the maintenance errors.
The crash occurred during a twilight scenic tour with four passengers on board: a newlywed couple from India, and a Kansas couple celebrating their 25th wedding anniversary. The helicopter departed McCarran International Airport in Las Vegas shortly before 4:30 p.m. local time, bound for the Hoover Dam.
The helicopter followed an established tour route until it was approximately 14 miles east of Las Vegas, at which point it began an abnormal left turn and climb, followed by a left turn and descent, according to radar data. It impacted the ground in mountainous terrain between Henderson and Lake Mead, killing the pilot and all passengers.
The pilot did not make any intelligible radio calls before the crash, and there was no cockpit voice recorder or flight data recorder on board the helicopter. According to NTSB chairman Deborah Hersman, investigators engaged in “a painstaking, deliberative investigation” that “ultimately led to the hangar floor” with the conclusion that improper maintenance was the cause of the fatal crash.
The NTSB found that, prior to the accident, Sundance Helicopters maintenance had been re-using degraded self-locking nuts that no longer met manufacturer specifications (although Sundance inspected its helicopters and corrected this practice shortly after the 2011 crash). Even so, according to investigator-in-charge Bill English, the disconnection of the control rod might have been prevented had a safety cotter pin been properly installed. However, neither the inspector who signed off on the maintenance, nor the pilot who performed a maintenance check flight of the aircraft before it returned to service, noticed the absence of the pin that investigators concluded had to be missing.
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