What happened
On a day visual flight rules flight near Nahanni Butte, Northwest Territories, a Robinson R44 Raven II helicopter, registration C-GNYT, attempted to land on a narrow mountain ridge. The aircraft, operated by Wild Water Heli-Fishing Ltd., was carrying a pilot and two passengers. While approaching the ridge, the pilot encountered turbulence and a loss of rotor speed.
To prevent the aircraft from striking a group of guides and hunters positioned near the landing site, the pilot attempted to abort the landing by turning 60 degrees away from the ridge. This maneuver caused the tail boom to strike the ground at an elevation of 4,600 feet. The impact sent the helicopter into a violent tumble down a 45-degree shale slope. The aircraft broke apart during the descent and was destroyed by a post-impact fire. The pilot survived with serious injuries, but both passengers sustained fatal injuries.
The investigation
Investigators examined the aircraft's performance capabilities and the environmental conditions at the time of the accident. The helicopter was operating at a weight of 2,385 pounds, which was within prescribed limits. However, the pressure altitude of the landing site left a very slim margin for hovering out of ground effect.
Technical inspections confirmed that the Robinson R44 Raven II was properly maintained and that the engine was producing full available power. There were no mechanical failures or flight control issues identified. The investigation also noted that the aircraft's emergency locator transmitter failed to transmit, likely due to the intensity of the post-crash fire.
Findings
- The shallow approach path placed the helicopter in subsiding air on the downwind side of the ridge, which increased the aircraft's sink rate.
- In an attempt to compensate for the increased sink rate, the pilot demanded more engine power than the aircraft could provide, leading to a loss of rotor speed.
- The pilot's decision to turn away from the ridge was motivated by the need to protect the ground party from potential injury.
- The tail boom strike on the ridge initiated the uncontrolled descent and subsequent destruction of the aircraft.