Incident Overview
The pilot reported a standard approach to a helicopter pad situated on a bluff overlooking a golf course. Approximately 100 yards from the pad and at 150 feet above ground level, he observed a twitch in the aircraft's nose and heard the engine rpm decreasing along with the engine spooling down. The pilot initiated an autorotation and turned the helicopter to the right to avoid rising terrain. The aircraft touched down hard, causing the landing gear to collapse and the tail rotor to strike the ground. After coming to a stop, the engine was still idling, so the pilot closed the fuel shutoff valve and throttle and turned off all electrical power. The engine required about 20 to 30 seconds to spool down.
Fuel Control Examination
The fuel control components were sent to the Allied Signal Materials Technology Center in South Bend, Indiana, for testing under the oversight of the Federal Aviation Administration. 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. The acceleration bellows assembly was identified as the probable source for the uncommanded minimum fuel flow condition. A leak was discovered in the bellows, which originated from a corrosion pit that penetrated through the outer ply of a convolution tube at the edge of a braze fillet. This pit caused evacuation and malfunction of the bellows.
Service Bulletin History
Allied Signal and Allison Engines issued service bulletins on November 18, 1993, concerning the replacement of the fuel control bellows. Allison Commercial Engine Bulletin CEB-A-282 directed that the beryllium copper bellows be replaced with 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.
Maintenance Records
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 Allison CEB-282. The records further indicated that the fuel control containing the beryllium copper bellows was reinstalled in the helicopter on October 1, 1997, at an engine time of 2,247.1 hours. The accident occurred 39 operating hours later.