What happened
On 3 August 2021, a Piper PA-28-140 with registration ZS-FWK departed Wonderboom Airport for a cross-country flight, intended to pass through Rustenburg and Zeerust before returning to its origin. The flight was conducted under Visual Flight Rules (VFR) by a pilot and one passenger.
While navigating a mountain range west of Rustenburg Airfield, the pilot attempted to climb from 6,500 feet to 8,500 feet. During this maneuver, the pilot noticed the altimeter was rising slowly. As the aircraft crossed the mountains, it encountered a tailwind and began to descend. Simultaneously, the airspeed indicator showed a rapid increase from 100 knots to 180 knots, exceeding the aircraft's maximum structural speed (Vne) of 155 knots. Despite attempts to reduce power, the high airspeed persisted.
Seeking a safe area, the pilot initiated a precautionary landing. During the final approach, the airspeed indicator still indicated 180 knots; however, upon attempting a go-around, the indicated speed dropped sharply to 60 knots. The pilot proceeded with a full landing. While the aircraft touched down successfully, the wing struck a wire fence during the landing roll, causing the aircraft to come to a stop with the wings entangled in the wire. There were no injuries to the occupants, though the aircraft sustained minor damage.
The investigation
SACAA AIID examined the aircraft's pitot-static system following the incident. A post-incident inspection by a maintenance engineer revealed that the pitot tube had been severed by the wire fence during the landing. Testing of the system showed that while the pitot port was clear, the static port was blocked, preventing airflow.
Records indicated that the pitot-static system had been inspected and found serviceable during a mandatory periodic inspection approximately 84 flight hours prior to the incident. The investigation also noted that the aircraft encountered a downdraft while crossing the mountain range, which triggered the descent that revealed the instrument malfunction.