What happened
On 24 May 2008, a Robinson R4-4 Raven II, registration ZS-SCV, was participating in the Annual Polokwane Fly-In. The pilot was conducting private pleasure flights for passengers near the SAPS hangar. During the takeoff sequence, the helicopter transitioned from a hover into forward flight at an altitude of approximately 3 meters. During this phase, the aircraft experienced a significant decay in main rotor RPM. In an attempt to maintain altitude, the pilot applied aft cyclic and raised the collective. This maneuver caused the tail rotor to strike the ground, leading the aircraft to roll over and subsequently catch fire. While the engine remained operational during the impact, the post-crash fire destroyed the airframe. The four occupants sustained minor and serious injuries, but there were no fatalities.
The investigation
An investigation by the SACAA AIID examined the flight dynamics and aircraft condition. Investigators reviewed video footage from the event, which confirmed that the engine had not failed during the accident. The footage revealed that the pilot initiated the takeoff with a 35-degree nose-down attitude. The investigation also confirmed that the aircraft was well-maintained, with only 17 airframe hours since new, and that the pilot held a valid license and medical certificate. Meteorological conditions were clear with light winds, and the aircraft was within its operational weight limits at the time of the incident.
Findings
- The primary cause of the accident was the loss of main rotor RPM during the takeoff transition.
- The power required for the maneuver exceeded the power available, leading to blade coning and further power demand.
- The pilot utilized an incorrect recovery technique; by raising the collective and flaring excessively, the pilot inadvertently increased the power demand and caused the tail rotor to impact the terrain.
- The aircraft was in a highly nose-down attitude during the initial takeoff phase, contributing to the unstable transition.