What happened
On 21 March 2019, a Tecnam P9/2 Echo, registration ZU-BJY, was conducting a training flight at Aeropark Zyn Kraal Aerodrome when a mechanical failure caused the aircraft to exit the runway. The flight, involving an instructor and a student pilot, began with a routine pre-flight inspection where the student pilot topped up the brake fluid. While the initial takeoff and subsequent training maneuvers proceeded without issue, the situation changed during the return to base.
During the landing phase, the instructor took control of the aircraft to stabilize the approach. Although the touchdown itself was successful, the aircraft experienced a total brakes failure during the landing roll. In an attempt to mitigate the loss of deceleration, the instructor shut down the engine to use aerodynamic drag to reduce speed. Despite these efforts, the aircraft overshot the runway and struck a perimeter fence, resulting in damage to the propeller blades.
The investigation
SACAA AIID investigators examined the aircraft's mechanical systems and maintenance history following the incident. Post-incident testing of the braking system revealed that while the system appeared functional under normal pressure, a leak was present when the brakes were applied forcefully. A disassembly of the brake master cylinder identified that the O-ring seals had failed.
Furthermore, the investigation scrutinized the maintenance practices of the Approved Maintenance Organisation (AMO). Investigators found that the aircraft's maintenance records lacked specific references to landing gear or brake system inspections. There was also no documented evidence in the flight logs regarding the frequency of brake fluid replenishment, which had been noted during the pre-flight inspection on the day of the accident.
Findings
- The primary cause of the incident was brakes failure resulting from worn-out O-ring seals in the brake master cylinder due to normal wear and tear.
- The incident was exacerbated because the crew did not report the high consumption of brake fluid, which was a clear indicator of an existing leak.
- The aircraft's maintenance records did not include landing gear or brake system inspections in the annual maintenance package.
- The AMO's in-house maintenance checklists were not fully aligned with the manufacturer's prescribed procedures regarding the brake system.
Safety action
- It is recommended that the AMO update its maintenance work packs and checklists to explicitly include the inspection and servicing of the brake system, ensuring alignment with the manufacturer's requirements and regulatory standards.