What happened
During a geological survey mission, a Hughes 369D helicopter, registration C-GYTY, was performing a descending turn to land at a sample collection site. The aircraft was transporting two passengers and a cache of geological samples. While executing a tight, clockwise descent from approximately 200 feet, the helicopter struck the hilly, rocky terrain at a high rate of descent and a 25-degree nose-down attitude.
The impact caused the right float and skid tube to dig into the ground, rupturing the internal fuel bladders. The aircraft bounced and tumbled approximately 60 feet from the initial impact point, followed by an intense fire fueled by spilled gasoline. The pilot was killed instantly upon impact, and while the two passengers survived the initial collision, they later died from their injuries.
The investigation
Investigators examined the wreckage, the Rolls-Royce Allison 250-C20B engine, and the fuel supply. The engine was found to be delivering power at the time of impact, and no pre-existing mechanical failures or fuel contamination were identified. The aircraft's maintenance records showed it had been properly inspected and was within weight and center of gravity limits.
Analysis of the flight path revealed that the pilot was performing a right-hand turn, a maneuver that likely obscured the view of the landing site due to the position of the passengers and the aircraft structure. The investigation also looked into aerodynamic phenomena, specifically vortex ring state and power turbine rpm (N2) droop, as potential contributors to the rapid descent.
Findings
- The helicopter experienced a high rate of descent during the final stages of the approach that the pilot could not arrest.
- The chosen approach pattern (a right-hand turn) hindered the pilot's ability to accurately judge necessary power and speed adjustments.
- Environmental and flight conditions, including light winds and a decelerating descent, were conducive to the development of vortex ring state or N2 droop.