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, the helicopter took off and began transitioning from a hover to forward flight. During this phase, the occupants heard a dull thud from the engine compartment, immediately followed by a violent, uncommanded yaw to the left. The pilot was unable to counteract the rotation, leading the aircraft to impact the ground on its left skid. The momentum of the impact caused the helicopter 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 pilot's maintenance records. The investigation established that the aircraft was within its approved weight limitations at the time of departure. While the pilot had performed a pre-flight inspection involving visual checks and manual rotation of the tail rotor, the aircraft's Authority to Fly (ATF) certificate had expired nine days prior to the accident.
Technical analysis focused on the tail rotor drive system. Investigators recovered the failed tail rotor drive belt from the wreckage. The inquiry revealed that the aircraft was still utilizing Gates-manufactured belts, despite existing Service Bulletins warning of premature wear and failure in these specific parts due to changes in manufacturing processes.
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 loss of tail rotor effectiveness rendered the helicopter uncontrollable, leading to the uncommanded yaw and subsequent impact.
- The aircraft was operating with an expired Authority to Fly certificate.
- The installed Gates belts were subject to known reliability issues, and the operator had not complied with Service Bulletins recommending their replacement.
Safety action
- It is recommended that the aircraft manufacturer provide specialized training to owners and operators regarding effective visual inspection techniques and the proper use of belt tension testing equipment to identify potential transmission system failures.