What happened
On 22 November 2008, a Robinson R44 Raven II, registration G-IGJC, was preparing for a private local flight from the general aviation apron at Liverpool Airport. The aircraft was carrying one pilot and three passengers. During the takeoff sequence, the pilot raised the collective control with more speed than usual, causing the helicopter to lift rapidly and begin a quick rotation.
In an attempt to correct the movement, the pilot applied right yaw pedal input. However, this action caused the aircraft to spin even faster. The pilot found it increasingly difficult to remain seated or maintain control of the aircraft, and the force of the rotation repeatedly threw him against the right cockpit door. To avoid a potential collision with other aircraft parked nearby, the pilot decided to descend toward the ground. The helicopter subsequently rolled over onto its left side, resulting in substantial damage to the rotor blades and the left cockpit area. The impact also damaged the engine cowling of another aircraft parked roughly 100 metres away.
Following the accident, the pilot and one passenger sustained minor injuries, while the remaining two occupants were unhurt. Emergency services attended the scene, and although some fuel leaked from the aircraft, no fire occurred.
The investigation
The AAIB examined the flight dynamics and the pilot's inputs during the critical moments of takeoff. While some witnesses were uncertain of the direction of the initial rotation, the investigation focused on the mechanical and aerodynamic response to the pilot's control inputs. The investigation also reviewed the maintenance history of the aircraft, noting that the helicopter had completed a scheduled inspection only 14 hours prior to the accident and was well within its maintenance interval.
Findings
- The primary cause of the accident was the rapid upward application of the collective control, which induced a sudden lift and yaw.
- The pilot's attempt to correct the rotation using right yaw pedal input actually increased the rate of the spin.
- While the aircraft would naturally tend to rotate clockwise (to the right) when the collective is raised, this tendency can be managed with left pedal input; however, the pilot's specific input exacerbated the instability.