What happened
On 2-5 August 2003, an Alouette II, registration ZU-RAL, was conducting a private aerial inspection of a farm in the Pongola area. After departing from a farm in the Saamwerk area, the pilot and a passenger headed toward Arizona Game Ranch to survey road conditions, erosion, and grazing lands.
During the mission, the aircraft climbed a valley to an altitude approximately 1,000 feet above the initial takeoff point. As the pilot reached the summit of the ridge, they attempted to pull back on the cyclic control to reduce airspeed and enter a hover. During this maneuver, the pilot noticed the aircraft was descending at a high rate. With engine power insufficient to maintain altitude, the pilot was forced to identify an emergency landing site. During the descent, the main rotor blades struck a tree near the ground, and the aircraft came to rest on the ridge. The subsequent shutdown of the rotors caused the blades to droop and strike the tree again, causing extensive damage to the main rotor head and all three blades.
The investigation
The investigation examined the flight conditions, the aircraft's maintenance status, and the pilot's experience. The Alouette II was operating under a valid Authority to Fly in the Special Experimental Category. Records showed the aircraft had undergone an inspection on 13 August 2003, with only 6.4 flight hours accumulated since that check.
The pilot had relatively limited experience on this specific type, having completed a conversion course involving 9.0 hours of dual training in June 2003. At the time of the incident, meteorological conditions were reported as fine with good visibility and light, variable winds.
Findings
- The primary cause of the incident was the pilot's failure to anticipate the impact of mountain waves, specifically the presence of downdrafts and tailwind components, which led to a critical loss of power while clearing the ridge.
- The pilot reported difficulty maintaining the aircraft's heading into the wind due to constantly shifting wind directions and a lack of visual cues regarding prevailing wind conditions.
- The phenomenon of vortex ring state was identified as a potential contributing factor to the rapid descent.