Ice buildup on a control mechanism caused a SkyMed helicopter to crash at the University Nebraska Medical Center in January 1988, according to the National Transportation Safety Board.

The board criticized Rocky Mountain Helicopter of Provo, Utah, for not installing covers on the helicopter's servo, or automatic control mechanism, after warnings in 1982 from the manufacturer that ice could accumulate there.The Jan. 20 crash could have been prevented, the NTSB said.

John Heiskell, director of operations for Rocky Mountain's medical group, said the company did not heed the manufacturer's warning because it was one of myriad non-mandatory service bulletins.

"There are hundreds of operational service bulletins in every aircraft we fly," he said.

If the company complied with every optional safety suggestion, the helicopters would never get out of the repair shops, Heiskell said.

Rocky Mountain reacts to bulletins based on the urgency with which they are sent, he said.

The NTSB also faulted the pilot, John Oldham, for not performing a thorough pre-flight check that could have detected the icy servo.

Heiskell said performing such a check would take 30 to 45 minutes, and spending that amount of time on a check defeats the medical helicopter's speed advantage.