LAS VEGAS (AP) - Federal crash investigators are focusing on inadequate maintenance as the cause of a twilight sightseeing helicopter crash that killed a pilot and four tourists near Las Vegas in December 2011.

The National Transportation Safety Board reviewed findings Tuesday in Washington, D.C., of a 13-month investigation of the Sundance Helicopters crash.

NTSB investigators say a crucial bolt worked loose in the rotor mechanism, causing a loss of control before the crash near Lake Mead.

Officials think the bolt wasn't properly secured during maintenance before the crash.

They note the mechanic and inspector had been called in early to do the work.

But the helicopter also passed other inspections before the crash.
Killed were two honeymooners from India, a Utica, Kan., couple celebrating their 25th wedding anniversary, and the pilot.

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