What happened
On 22 April 2014, a Piper PA-46-310P (registration ZS-LLD) departed Cape Town International Airport on an IFR flight bound for Swartwater, Limpopo. Shortly after the aircraft began climbing through 13,500 feet, Air Traffic Control (ATC) alerted the pilot that the aircraft's Mode C transponder was transmitting incorrect altitude data, suggesting a descent while the aircraft was actually ascending.
Despite attempts by the pilot to rectify the issue by recycling the transponder, the erroneous data persisted. During the flight, the aircraft's airspeed exceeded both the Maximum Structural Cruising Speed (VNO) and the Calibrated Never Exceed Speed (VNE). This led to a catastrophic in-flight breakup. The wreckage was discovered scattered across a 1.58km path in the mountainous terrain of Farm Rooisand, Northern Cape. Both occupants sustained fatal injuries.
The investigation
SACAA AIID investigators examined the aircraft's flight path, wreckage, and instrument systems. The investigation focused on why the aircraft's flight control surfaces failed and why the pilot was receiving misleading information.
Data from the aircraft's GPS confirmed that the Mode C transponder had been transmitting incorrect altitude information for approximately one hour and 48 minutes prior to the accident. Investigators also analyzed the pitot-static system, noting that the aircraft had previously operated on gravel runways, which could have introduced foreign matter into the instruments. While the pitot head showed evidence of contamination, the exact source of the blockage could not be definitively confirmed due to the nature of the impact.
Findings
- The aircraft exceeded its VNO and VNE speed limits, which caused the failure of the flight control surfaces.
- The primary cause of the overspeed was erroneous airspeed and altitude indications caused by a blockage of the pitot tube by dust and sand.
- The pilot was unaware that the cockpit instruments were providing incorrect airspeed readings due to the conflicting data being transmitted via the transponder.
- The aircraft was within weight and balance limits and had sufficient fuel for the intended mission at the time of departure.