What happened
On the morning of 29 August 2023, a Tri Cubby with registration ZU-EIB departed Swellendam Aerodrome (FASX) for Worcester Aerodrome (FAWC) in the Western Cape. The aircraft had previously flown from Worcester to Swellendam earlier that day for maintenance work involving the replacement of rudder cables. During the return leg, while flying over the Robertson area, the aircraft encountered intense atmospheric disturbances. An eyewitness observed the aircraft spinning and descending in a steep, nose-down attitude before impacting a farm near Robertson. The impact triggered a post-crash fire that destroyed the aircraft, and the pilot was fatally injured.
The investigation
SACAA AIID investigators examined the wreckage and the flight conditions at the time of the accident. The investigation established that the aircraft was operating in an area prone to significant mountain wave turbulence. The aircraft's design required the pilot to fly from the rear seat to compensate for a center of gravity positioned forward of the limit. Investigators also noted that the pilot had placed an overnight suitcase and various bags on the front seat of the tandem cockpit. Evidence suggested that the aircraft experienced an abrupt flight upset due to the weather, which led to a critical mechanical interference within the cockpit.
Findings
- The primary cause of the accident was the aircraft encountering mountain wave turbulence, which triggered an abrupt maneuver.
- This turbulence caused luggage placed on the front seat to shift forward against the control column.
- The weight of the shifting luggage physically pushed the column forward, preventing the pilot from applying back-pressure to recover the aircraft.
- The aircraft entered a nose-dive and subsequent stall/spin sequence that was unrecoverable.
- The pilot had not sufficiently secured the luggage to prevent it from sliding during flight or failing to account for the potential forward tilting of the seat backrest.
- Severe turbulence was present in the region, as confirmed by other aircraft operating in the vicinity at the same time.