What happened
On December 29, 2019, a Robinson R44 Raven II was conducting a non-commercial cross-country flight toward a destination near the Castle of Wijnendale. During the final approach, the pilot was alerted by the activation of the low rotor RPM warning horn. In response to the emergency, the pilot initiated an emergency descent.
As the helicopter approached the ground in a cultivated field, the rotor lacked sufficient energy to cushion the touchdown. The aircraft's skids sank into the muddy terrain, causing the helicopter to stop abruptly. This sudden deceleration caused the airframe to tilt forward onto its right side, resulting in the main rotor striking the ground. While the occupants escaped the wreckage without injuries, the helicopter was destroyed.
The investigation
The AAIU(Be) examined the technical condition of the aircraft and the pilot's training history. Investigators found that the engine and V-belt drive system were functioning normally prior to the event, but the impact itself damaged the V-belt drive.
Crucially, the investigation scrutinized the pilot's training at a registered flight training organization. Although the Robinson Helicopter Company's Operational Suitability Data (OSD) had mandated specific training elements regarding low rotor RPM recognition and recovery since 2015, the investigation found that these requirements had not been integrated into the pilot's 2019 training program. Furthermore, the pilot's initial skill test had focused on autorotation performance but had not specifically tested the ability to recognize or recover from a low rotor RPM state.
Findings
- The primary cause of the accident was the pilot's inability to properly recognize and respond to the low rotor RPM condition.
- The pilot's training and skill testing lacked the mandatory elements required by the R44 Operational Suitability Data (OSD).
- The helicopter did not regain sufficient rotor RPM during the descent, leaving inadequate energy for a soft landing.
- The muddy ground conditions contributed to the abrupt stop and subsequent nose-over of the aircraft.
- The training organization had failed to implement mandatory training and awareness elements regarding rotor RPM decay and energy management.
Safety action
Following the identification of a safety issue regarding non-compliant training standards, the AAIU(Be) issued safety recommendation BE-2022-01. This recommendation calls on the Belgian Civil Aviation Authority (BCAA) to ensure that all organizations conducting Robinson R44 training properly implement the mandatory training elements defined in the OSD RTR 465.