HONOLULU -- The National Transportation Safety Board on Thursday issued its preliminary report on the March 8 Heli USA crash at Princeville on Kauai that killed four people and left three seriously injured.

From initial findings, the NTSB noted a possible problem with part of the tour helicopter's hydraulic system.

Before the A-Star slammed into the ground nose first searing off its entire front, pilot Joe Sulak knew he was in trouble. The NTSB report said Sulak first reported hydraulic problems, then hydraulic failure.

Then just before the helicopter crashed, without explanation the pilot told the dispatcher: "OK, we're done."

The NTSB initial report found the hydraulic system was OK, the pump intact, drive belt attached, hydraulic reservoir full, except for possible problems with the left lateral servo.

The servo is part of the helicopters hydraulic system, like power steering in a car. The system makes it easier to control the helicopter.

The Federal Aviation Administration on Thursday sent out this directive to all operators of A-Stars nationwide, telling them to double check their servos. The FAA said it has become aware of potential for separation or excessive wear and tear on servo bodies.

The FAA said the warning of a potential safety hazard with servos is related to two earlier A-Star crashes, not the Princeville crash.

"It is really too early to say what the cause of the crash is. NTSB and FAA are still investigating it, and it's too early for us make any comments," FAA spokesman Ian Gregor said.

The NTSB has sent the Heli USA's entire hydraulic system, including the servos to its lab in Washington for further investigation.

It is expected to take at least a year to get a final report.