What happened
On 9 October 2021, a private flight departing from Morning Star Aerodrome in the Western Cape ended in an uncontrolled descent. The pilot, accompanied by one passenger, was operating a RotorWay Executive 162F helicopter, registration ZU-RDX, under visual meteorological conditions.
Following a standard pre-flight inspection where all checks appeared normal, the pilot transitioned the aircraft from a hover to forward flight. During this phase, an audible thud was heard from the engine compartment, immediately followed by a violent, uncommanded yaw to the left. The pilot was unable to counteract the rotation, leading the helicopter to impact the ground on its left skid. The momentum of the impact caused the aircraft to roll onto its right side, during which the main rotor blades struck and severed the tail boom. Despite the substantial damage to the aircraft, there were no injuries to the pilot or the passenger.
The investigation
SACAA AIID investigators examined the wreckage and the circumstances leading to the impact. The investigation confirmed that the aircraft was within its maximum takeoff weight at the time of the accident. While the pilot had performed a pre-flight inspection using a tensioning tool, the investigation revealed that the aircraft's Authority to Fly (ATF) certificate had expired nine days prior to the incident.
Technical analysis focused on the tail rotor drive system. Investigators recovered the tail rotor drive belt from the wreckage and found that it had been severed. The investigation also looked into the maintenance history and the specific components used in the transmission system.
Findings
- The primary cause of the accident was the severing of the V-belt during the transition to forward flight, which resulted in the immediate failure of the tail rotor.
- The failure of the tail rotor rendered the helicopter uncontrollable, leading to the loss of directional stability.
- The aircraft was equipped with Gates-manufactured belts, which had been the subject of manufacturer Service Bulletins due to premature wear and failure.
- The operator had not complied with the Service Bulletin regarding the replacement of these specific belts.
- The aircraft was not in an airworthy state because the ATF certificate had expired.