What happened
On 17 June 2013, a Bantam B22J microlight, registration ZU-CZU, was conducting a private flight from Ingwe private aerodrome to Aero Den aerodrome in the North West province. Approximately 15 minutes after departure, the pilot detected engine-related vibrations and decided to return to Aero Den for a precautionary landing. During the approach, roughly half a and mile from the runway, the propeller became loose and began striking the engine. The pilot responded by shutting down the engine, resulting in a hard landing on runway 18. While the pilot escaped without injury, the aircraft sustained substantial damage to the undercarriage and the engine area.
The investigation
An investigation by the SACAA AIID examined the aircraft's components and maintenance history. Metallurgical analysis of the propeller assembly revealed that the propeller was held by only a single bolt, as the other five bolts had failed. The investigation found that the bolts had been installed with the threaded ends facing aft, which contradicted the manufacturer's prescribed assembly method. Additionally, the required Belleville or flat washers were missing from the assembly. The investigation also noted that the aircraft had previously undergone engine and propeller flange work following a propeller strike, and the bolts showed signs of being refitted multiple times.
Findings
- The primary cause of the accident was an unsuccessful forced landing following the mechanical failure of the propeller.
- Improper maintenance procedures were a significant contributing factor, as the propeller bolts were not installed according to the Jabiru propeller manual.
- The pilot's flying licence and medical certificate were both invalid at the time of the occurrence.
- The maintenance organization failed to supervise work correctly, allowing for the use of incorrect assembly techniques and missing hardware.