WASHINGTON Jan 29 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
"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
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
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
"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
A synopsis of the NTSB report, including the probable cause,
findings, and a complete list of the safety recommendations, is