The National Transportation Safety Board is calling for establishing new duty-time regulations covering maintenance workers involved in on-demand, fractional and all repair station operations, along with those involved with scheduled carriers.

The recommendation is one of three new ones issued today (Jan. 29) following the safety board’s investigation of the Dec. 7, 2011 crash of a Eurocopter AS350-B2 helicopter operated by Sundance Helicopters on a sightseeing trip outside Las Vegas. The pilot and four passengers were killed.

The safety board cites inadequate maintenance as the probable cause of the accident, and finds that mechanic and inspector fatigue played a contributing role.

The helicopter, N37SH, had undergone a 100-hr. inspection the day before the accident and the fore/aft servo was replaced. But investigators believe that the input rod and fore/aft servo became disconnected shortly before the crash, leading to a loss of control. The fore/aft servo is connected to the input rod by a bolt secured by a self-locking castellated nut and a split pin.

The maintenance technician indicated that the work had been accomplished as required, and a company inspector approved the work. NTSB believes a bolt had been in place connecting the servo with the input rod, since control of the aircraft would not have been possible otherwise.

But the safety board believes the self-locking nut became separated from the bolt, likely because it was worn. The safety board further believes that the split pin, the second securing device, either was not installed or had been improperly installed.

Investigators found that both the mechanic and inspector had been called in to work on a shift that they had been scheduled to be off, and hours earlier than they normally work.

Both were on duty before 6 a.m., and each had worked longer than 12-hr. shifts. Both knew proper procedures for correct installation, the safety board notes. “If the work shifts of the maintenance personnel had been consistent, a major source of their fatigue could have been mitigated,” the NTSB says.

“In too many investigations we have seen the tragic results of human error, and we’ve long known about the safety challenges unique to maintenance – tasks performed at night (when our bodies are programmed to rest), long duty days, shift changes and interruptions, the disassembly and reassembly of complex systems, time pressures and more,” says NTSB Chairman Deborah Hersman.

Hersman notes the attention given to the flight crew and the major effort recently undertaken to update flight and duty time regulations for Part 121. But she says this attention also needs to be given to other safety-sensitive areas.

NTSB had previously made recommendations covering duty time limitations in maintenance, and the issue was debated in the late 1990s. At the time, the consensus was that more studies were necessary. But board member Mark Rosekind notes those studies have been accomplished. “What’s frustrating to us is we are going at this piecemeal,” he says of duty and rest regulations. “We knew this was an issue a decade ago and haven’t seen any action.”

In addition to improper installation of the bolt, the safety board cites as the probable cause the improper use of the bolts and nuts. Manufacturers provide detailed instructions on proper torque and reuse of nuts and bolts. But some of the nuts found at the crash site were worn beyond manufacturer guidelines for reuse. A subsequent investigation of 13 Sundance helicopters found that half of the nuts did not meet requirements.

This led to FAA releasing a general aviation maintenance alert in November about proper use of hardware such as nuts and bolts, and the agency is preparing a second, broader aviation alert on the same subject to be released earlier this year.

Sundance has since changed its policy to prohibit the reuse of the nuts.

Board member Robert Sumwalt further questions FAA’s role in providing adequate oversight. “Where were they? They weren’t there,” he says, adding, “Things that [are] getting attention are those things that get done properly.”

NTSB issued three recommendations to FAA: establish duty time regulations for maintenance personnel in Parts 121, 135, 91 (K) and 145 that cover start time, workload, shift changes, circadian rhythms, adequate rest time and other factors; encourage operators to implement best practices for conducting maintenance under Parts 121, 135 and 91 (K) that include use of work cards to detail maintenance tasks and other recording and verification of each task; and mandate maintenance personnel to receive initial and recurrent human factors training that cover human error causes such as fatigue.