NTSB Identification: LAX98LA053.
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Accident occurred Saturday, December 06, 1997 in SAIPAN, India
Probable Cause Approval Date: 02/28/2000
Aircraft: McDonnell Douglas 369HS, registration: N9068F
Injuries: 5 Minor.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot reported that he was making a standard approach to the helicopter pad which was located on a bluff overlooking a golf course. About 100 yards from the pad and 150 feet agl, he noticed a twitch in the nose of the aircraft and heard the rpm decreasing and the engine spooling down. He entered an autorotation and turned the helicopter to the right to avoid upsloping terrain. The aircraft touched down hard and the landing gear collapsed and the tail rotor struck the ground. The pilot stated that after coming to a stop, the engine was still idling so he closed the fuel shutoff valve and throttle and turned off all electrical power. The engine took about 20 to 30 seconds to spool down. The fuel control components were then tested at the Allied Signal Materials Technology Center in South Bend, Indiana, under the auspices of the FAA. Operational bench tests performed on the fuel control and governor indicated that the fuel control would meter minimum fuel flow throughout the various test points and that the acceleration bellows assembly was the probable source for the uncommanded minimum fuel flow condition. A leak was found in the bellows which stemmed from a corrosion pit that penetrated through the outer ply of a convolution tube at the edge of a braze fillet. The pit caused evacuation and malfunction of the bellows. Allied Signal and Allison Engines issued service bulletins on November 18, 1993, regarding the replacement of the fuel control bellows. The Allison Commercial Engine Bulletin CEB-A-282 directed that the beryllium copper bellows be replaced by a stainless steel welded Pc Inconel Bellows the next time the affected fuel control was at a repair/overhaul facility and the bellows area was disassembled for any reason, but in no case later than the next fuel control unit overhaul. The aircraft maintenance records revealed that on April 22, 1997, an overhaul of the fuel control assembly was performed. On a form indicating compliance with applicable service bulletins and directives, 'NA' was written by the maintenance facility in the space next to the listing for the Allison CEB-282. The records revealed that the fuel control with the beryllium copper Pc bellows was reinstalled in the helicopter on October 1, 1997, at engine time 2,247.1 hours, 39 hours prior to the accident.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The failure of the maintenance facility to comply with the service bulletins, which resulted in the development of a corrosion pit, subsequent leakage and failure of the acceleration bellows of the fuel control.

Full narrative available

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