LAS VEGAS (AP) - Federal crash investigators say mechanics and inspectors should use work checklists to avoid maintenance errors like one they say caused a fatal sightseeing helicopter crash outside Las Vegas in December 2011.
The National Transportation Safety Board ruled Tuesday in Washington, D.C., the Sundance Helicopters crash was caused by a crucial locking nut working loose in the rotor mechanism.
That caused a loss of control before the crash near Lake Mead killed the pilot and four tourists.
Officials think a fatigued mechanic improperly installed the nut during maintenance before the crash.
They note the mechanic had been called in early to do the work.
But the helicopter also passed inspections prior to the crash.
Killed were two honeymooners from India, a couple from Utica, Kan., and the 31-year-old pilot.