What happened
On 23 September 2021, a Schweizer 269C helicopter, registration ZS-HEW, was conducting a game capture operation within the Camdeboo Game Reserve in Graaf-Reinet. The flight, operated by E’scape Airtours Charters and Transfer CC, was a short-duration mission intended to return to the same landing site after completion.
While flying at approximately 200 feet above ground level, the pilot experienced intense vibrations through the tail rotor pedals. Recognizing the severity of the issue, the pilot immediately initiated an autorotation, successfully bringing the aircraft down in an open field. While the pilot escaped the serious incident without injury, the helicopter sustained substantial damage to its stabilizer and tail rotor assembly.
The investigation
An investigation by the SACAA AIID focused on the mechanical integrity of the tail rotor assembly and the maintenance history of the aircraft. Metallurgical analysis revealed that the failure originated from a fatigue fracture in the shank section of the fork hinge bolt. The testing also identified evidence of rotation within the assembly, which created localized surface damage known as stress raisers, further accelerating the fracture process.
Investigators examined the maintenance records and found that while the bolt used was the correct part number according to manufacturer service bulletins, there was no evidence that required torque inspections had been performed. Specifically, the investigation found that the mandatory torque checks required by FAA Airworthiness Directive DCA/HU269/74—which must be conducted at 25-hour intervals following modification and every 300 hours thereafter—were not being documented or performed.
Findings
- The primary cause of the incident was a fatigue fracture of the fork hinge bolt, which created a significant imbalance in the tail rotor.
- The maintenance organization failed to adhere to the required intervals for torque check inspections as mandated by the relevant Airworthiness Directive.
- Because the necessary inspections were not carried out, the Certificate of Release to Service issued in August 2021 was considered invalid.
- The investigation noted that the SACAA had issued a Certificate of Airworthiness without verifying that all manufacturer-released Service Bulletins and Airworthiness Directives had been incorporated by the maintenance provider.
- Potential contributing factors to the bolt's failure included possible under-torquing, worn or collapsed washers, or improper assembly during maintenance.