WASHINGTON, Jan 29 (Reuters) - The U.S. National Transportation Safety Board said on Tuesday improper maintenance was the likely cause of a Dec. 7, 2011, sightseeing helicopter crash near Las Vegas that killed the pilot and four passengers.
The board said its investigation of the crash of a Sundance Helicopters Eurocopter AS350 found inadequate maintenance, including degraded material, improper installation and inadequate inspections.
"This investigation is a potent reminder that what happens in the maintenance hangar is just as important for safety as what happens in the air," NTSB Chairman Deborah Hersman said in a statement.
The helicopter, operating as a "Twilight City Tour" air tour, crashed in mountainous terrain about 14 miles (23 km) east of Las Vegas on Dec. 7, 2011, less than 10 minutes after it left Las Vegas McCarran International Airport en route to Hoover Dam.
The NTSB said the accident occurred after one critical flight control unit separated from another, which sent the helicopter first higher, then into a sharp descent at a rate of at least 2,500 feet per minute.
The NTSB found that the crash was the result of Sundance Helicopters' improper reuse of a degraded self-locking nut, and the improper or nonuse of a split pin to secure the degraded nut, in addition to an inadequate post-maintenance inspection.
The investigation found that both the mechanic and the post-maintenance inspector were fatigued and did not have clearly delineated steps to follow on a "work card" or "checklist."
As a result of the crash, the NTSB said it made, reiterated and reclassified recommendations to the Federal Aviation Administration about the need for improved maintenance documentation.
"One of the critical lines of defense to help prevent tragedies like this crash is improved maintenance documentation through clear work cards, or checklists," Hersman said. "Checklists are not rocket science, but they can have astronomical benefits."
A synopsis of the NTSB report, including the probable cause, findings, and a complete list of the safety recommendations, is available at www.ntsb.gov/news/events/2013/las_vegas_nv/index.html