NTSB: Loose lock nut caused fatal helicopter accident at Lake Mead

A worn lock nut came loose in a Sundance tour helicopter, causing the rotor craft to spin upward out of control before it made a sharp turn, rapid descent and slammed into a ravine near Lake Mead on Dec. 7, 2011, killing all five on board, the National Transportation Safety Board said Tuesday.

In a probable cause summary, investigators for the safety board blamed the sightseeing helicopter crash on "inadequate maintenance, including degraded material, improper installation, and inadequate inspections."

They determined that a self-locking nut in the rotor mechanism had been reused in violation of guidelines.

"The investigation revealed that Sundance Helicopters' maintenance personnel were reusing nuts that did not meet the criteria specified by Eurocopter and FAA (Federal Aviation Administration) guidance," according to the accident report's executive summary. The summary doesn't include the board's rationale for the conclusions.

Other contributing factors were "the improper or non-use of a split pin (or 'cotter pin') to secure the degraded nut, in addition to an inadequate post-maintenance inspection."

NTSB Chairwoman Deborah A.P. Hersman said, "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."

Sundance Helicopters Chief Executive Officer Bob Engelbrecht said in a statement that when the final report is published in several weeks, "We will study the report closely, review the findings and recommendations, and look to further improve our processes and procedures."

Engelbrecht noted that Sundance is "the most experienced and long-standing helicopter tour operator in Las Vegas, and we are prepared to work with the NTSB and the FAA to continue to improve the safety of our operations."

Killed in the crash, 14 miles east of Las Vegas, were Lovish Bhanot, 28, and Anupama Bhola, 26, a honeymooning couple from India; Delwin and Tamara Chapman, both 49, a couple from Utica, Kan., who were celebrating their 25th wedding anniversary; and the 31-year-old pilot, Landon Nield.

Gary Robb, a Kansas City, Mo., attorney who filed wrongful death lawsuits in Clark County District Court for families of the couples, said the tragedy occurred because of "an inexcusable mistake."

"This is like a vehicle mechanic putting a wheel on a car without lug nuts," Robb said. "What we have here is horribly inadequate maintenance that allowed this critical part to be reused too many times."

Robb won a $38 million settlement in 2005 for Chana Daskal of New York, who was severely burned and injured when a Papillon Airways sightseeing helicopter crashed near Meadview, Ariz., in 2001, killing six.

In the 2011 crash, Sundance Helicopters' Eurocopter AS350-B2 was returning to McCarran International Airport from a twilight flight over Hoover Dam and Lake Mead when it suddenly made the strange maneuver before plunging into a narrow ravine in the River Mountains and broke into tiny pieces and burned.

"I know what happened to my brother can't be changed," the pilot's sister, Angalena Adams, said Tuesday after watching a webcast of an NTSB hearing on the crash from her home in Cedar City, Utah. "But I hope Sundance has fixed the problems that were wrong."

Investigators found the accident occurred after a critical flight control unit separated from another, sending the helicopter out of control.

"After the part separated, the helicopter climbed about 600 feet, turned about 90 degrees to the left, descended about 800 feet, began a left turn, and then descended at a rate of at least 2,500 feet per minute to impact," the executive summary reads.

The Associated Press contributed to this report.