A critical control device came loose on the Heli USA AStar helicopter that crashed at Princeville Airport March 8, killing four people, including pilot Joe Sulak, and seriously injuring three others, according to a preliminary report released yesterday by the National Transportation Safety Board.

Shortly before the crash, Sulak radioed that he was "having hydraulic problems" and was going to attempt an emergency landing. He later changed his description to a hydraulic "failure."

Moments after that, in his final radio transmission, Sulak said, "OK, we're done."

The helicopter was coming in about 10 feet over the runway when it turned slowly to the left, tipped onto its nose and crashed heavily into the grassy apron, breaking its main rotor blades, crushing the front of the helicopter cabin and causing the AStar's floats to inflate, the NTSB report said.

Separate statements issued by the Federal Aviation Administration and AStar manufacturer Eurocopter said the failure of the control device, known as a "rotor control servo," can result in a pilot's loss of ability to control the AStar helicopter. Both the FAA and Eurocopter issued statements to flyers about maintenance of the part this week.

The FAA said its statement was not prompted by the Heli USA crash, and Eurocopter did not identify the crash to which it was responding.

The FAA report said a similar failure has resulted in two previous fatal crashes. The FAA bulletin was e-mailed yesterday to owners and operators of various models of the Eurocopter AS350 aircraft, saying the failure of a metal washer could cause a helicopter to crash.

The washer is part of the mechanism that prevents the unscrewing of one end of a hydraulic "servo-control rod." An AStar has three of these units that change the tilt of the helicopter's main rotor assembly. The washer has a small tang extending into its center hole, which locks it into a groove in a threaded shaft. In some cases, the tang has been found broken or worn away, allowing the threaded shaft to vibrate loose from the servo control rod.

INSPECT NOW

The FAA yesterday "strongly" recommended that mechanics and pilots conduct immediate inspections, check for worn parts and report specific problems to the FAA. Eurocopter, two days earlier, had telexed a warning to its customers about assembling the lower part of the main rotor servo-control.

FAA regional spokesman Ian Gregor said the airworthiness bulletin was "some time in the making" and was being worked on before the Heli USA crash occurred. He said the two fatal air crashes cited in the bulletin predate the March 8 crash.

Heli USA President Nigel Turner said his mechanics checked all Heli USA AStars in Hawai'i and on the Mainland within days of the crash, and found none with problems like the ones described in the NTSB report and the FAA and Eurocopter notices.

"We checked the day after, and we went through all the fleet and we found nothing like this on any aircraft," Turner said.

He said he could not address the technical issues involving the assembly and maintenance of the unit.

"I'm not a mechanic. I'm a pilot. And I can't make a comment at this time because it's early in an investigation. They are diligently working in Washington" to study the cause of the wreck, he said.

NO CONCLUSIONS YET

The NTSB report does not suggest that the detached servo connection caused the crash. It is a preliminary report, and the determination of probable cause of the Heli USA AStar crash is months and perhaps more than a year off. NTSB air safety investigator Brian Rayner will make a report, which will be reviewed by the full safety board before the probable cause report is issued.

Various parts of the aircraft have been removed and shipped to laboratories on the Mainland for testing. Rayner said the entire engine will be tested, and perhaps actually run. Parts of the hydraulic system have been removed for testing, in part because Sulak reported a hydraulic problem before the crash. The servo unit also has been shipped off for study.

On the day of the crash, Sulak took off from Princeville Airport at 2:15 p.m. with three married couples on board: Joe and Veronica O'Donnell of East Rockaway, N.Y., Cornelius Scholtz and Margriet Inglebrecht, of Santa Maria, Calif., and Teri and James McCarty of Cabot, Ark.

Sulak, John O'Donnell, Teri McCarty and Inglebrecht were killed as the helicopter returned from the planned 45-minute flight.

'I'M HAVING ... PROBLEMS'

The Heli USA dispatcher told investigators that 40 minutes into the flight, at 2:55 p.m., Sulak said on the radio, "I'm having hydraulic problems, and I'm probably going to have to do a run-on landing."

The standard procedure on an AStar whose hydraulics have failed is to land with a little forward speed, so the helicopter slides to a stop on its skids.

Rayner's report does not describe any obvious failure with the aircraft's hydraulics. The hydraulic pump was reported intact, its drive belt still attached and its fluid reservoir full.

The only obvious physical problem, other than damage clearly due to the wreck, was the helicopter's left lateral flight control device was loose.