Engine failure leads to helicopter rollover during autorotation

Casualties unknown • Dawson, Yukon 60 nm North, CA

A Bell 206B helicopter experienced a sudden engine failure during low-altitude flight, resulting in a rollover and substantial aircraft damage.

What happened

While flying at approximately 100 feet above ground level, the pilot of a Bell 206B helicopter was transiting from an exploration camp to a nearby worksite to collect personnel. During the cruise phase of the flight, the engine suddenly lost power without any prior warning or instrument indications.

In an attempt to manage the emergency, the pilot performed an autorotation, attempting to stretch the glide to clear a creek and reach a suitable landing area. However, this maneuver caused the rotor RPM to decline, leading to a loss of lift. Upon touchdown, the left skid caught the ground, causing the aircraft to roll onto its right side. While there were no injuries, the helicopter sustained substantial damage.

The investigation

Investigators examined the wreckage and found that the engine had ceased operation due to fuel starvation. While the fuel supply was sufficient and the fuel lines were free of contaminants, a critical failure was identified in the engine-driven fuel pump (EDP).

Field examination revealed that the drive shaft of the pump could rotate, but it was no longer driving the internal pumping gears. This was caused by excessive wear on the splines of both the drive shaft and the driver gear. This specific pump model, the MFP263, had accumulated approximately 6,555 hours of service.

Further analysis by the manufacturer and investigators found oxidized metal powder from the splines within the fuel filter. The investigation also noted that this was one of three similar pump failures reported within a single week. While the use of Jet B fuel—which has lower lubricity than Jet A—was noted, the exact cause of the accelerated spline wear could not be determined.

Findings

  • The engine failure was caused by the disengagement of the fuel pump drive shaft from the driver gear due to spline wear.
  • The pilot's low altitude at the time of the failure limited available landing options.
  • The decision to stretch the glide to avoid a creek resulted in a loss of rotor RPM, contributing to the uncontrolled touchdown.

Safety action

Following the incident, the Allison Engine Company issued a Commercial Engine Bulletin. This directive required the inspection of affected fuel pumps for drive shaft backlash, with mandatory recurring inspections every 100 hours.

Probable cause

The engine lost power because the engine-driven fuel pump failed due to the disengagement of the drive shaft splines from the driver gear caused by excessive wear. The pilot's low altitude and the subsequent loss of rotor RPM during the glide maneuver contributed to the impact.

Frequently asked questions

What happened in the 1997-07-24 Bell 206B (Helicopter) C-FNIQ accident near Dawson, Yukon 60 nm North, CA?

A Bell 206B helicopter experienced a sudden engine failure during low-altitude flight, resulting in a rollover and substantial aircraft damage.

What aircraft was involved and where did it happen?

The accident on 1997-07-24 involved a Bell 206B (Helicopter) C-FNIQ, operated by Fireweed Helicopters Ltd., at Dawson, Yukon 60 nm North, CA.

What was the probable cause of the accident?

The engine lost power because the engine-driven fuel pump failed due to the disengagement of the drive shaft splines from the driver gear caused by excessive wear. The pilot's low altitude and the subsequent loss of rotor RPM during the glide maneuver contributed to the impact.

Loading the flight search…