ASN Wikibase Occurrence # 343105
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| Date: | Monday 25 June 1990 |
| Time: | |
| Type: |  Bell 204B |
| Owner/operator: | Canadian Helicopters |
| Registration: | C-FBHY |
| MSN: | 2010 |
| Year of manufacture: | 1963 |
| Fatalities: | Fatalities: 0 / Occupants: 3 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | near Hay River, Northwest Territories -
 Canada
|
| Phase: | Unknown |
| Nature: | Ferry/positioning |
| Departure airport: | |
On arrival at Hay River, the helicopter overflew the forestry base at about 400ft. agl. The pilot then turned onto final approach and had reduced power to begin a descent when he noticed the cyclic control feeling 'sloppy'. He then noted the power turbine (N2), main rotor, and gas producer turbine (N1) RPM at 70 percent. The pilot selected the governor switch to the emergency position while the throttle was full open, but got no response. The pilot was unable to reach a suitable landing area to conduct an emergency landing. The helicopter touched down amongst trees, breaking into three sections with the main fuselage area coming to rest at a 75deg. angle to the left. There was no observed rotational damage to the tail rotor or tail rotor drive shaft. None of the occupants reported any unusual noises or warning lights prior to, or during the occurrence. Evidence found at the accident site indicated that the helicopter struck the ground at a very high rate of descent. This was a result of the main rotor RPM decaying to 70 percent before the pilot became aware that he had an engine malfunction. Although the Flight Manual found in the helicopter indicated that it was equipped with a main rotor low RPM horn and light warning system, one was not installed. A pilot would have become aware of a loss of engine power sooner, had a main rotor low RPM warning system been installed. The engine was removed from the helicopter for testing and disassembly. Disassembly of the main fuel regulator revealed that the differential maximum fuel flow stop lever had become loose and fallen down into the unit, contacting the N1 governor flyweights. Numerous marks were apparent on the flyweights as well as on the lever. The lever pivoted on a pin which was held in place with a strand of lockwire. The pin had backed out of position, past the lockwire and allowed the lever to fall out of position.The irregularities found within the main fuel regulator could not have been caused by impact damage. Wear along the pin hole allowed the pin to slip past the lockwire, allowing the differential maximum fuel flow stop lever to move freely. Interference of the lever with the N1 governor flyweights caused the reduction in engine power. When the pilot selected the governor switch into the emergency position he should have been able to recover the lost power by operating the throttle manually. This would have taken several seconds and there may not have been enough time remaining before impact with the ground.
Sources:
WAAS
Revision history:
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