Aircraft and Flight Information
A Piper PA-28-140, registration ZS-FWK, was involved in a serious incident on 3 August 2021. The aircraft had accumulated 12,120.65 total airframe hours. The flight was conducted under Part 91 of the Civil Aviation Regulations as a private cross-country flight with a pilot and one passenger on board. The pilot held a valid Private Pilot Licence (Aeroplane) and had 144 total flying hours, with 134 hours on type.
Sequence of Events
The flight departed from Wonderboom Airport (FAWB) at approximately 1400Z, routing via waypoint UTRUK, Rustenburg Airfield (FARG), and Zeerust Airfield (FAZR), with the intention to return to FAWB. A VFR flight plan was filed. While flying over FARG, the pilot initiated a climb from 6,500 feet to 8,500 feet to clear a mountain range west of FARG. During the climb, the altimeter indicated a slow rise, and the aircraft reached 7,500 feet overhead the mountains. The pilot then encountered a tailwind, and the aircraft began to descend while the airspeed indicator increased from 100 knots to 180 knots. The pilot reduced power twice but could not slow the aircraft. A suitable area was selected for a precautionary landing. On final approach, the airspeed still showed 180 knots. When the pilot added power for a go-around and the aircraft climbed, the airspeed dropped to 60 knots. The pilot then committed to a full landing. The aircraft touched down successfully, but during the landing roll struck a wire fence, causing the wings to become entangled. The aircraft came to rest in that position. The pilot and passenger were not injured.
Post-Incident Inspection
Minor damage was sustained, including scratches on both wings and the windscreen. Inspection revealed that the pitot tube, installed on the underside of the left wing, had been severed by the wire fence during the landing roll. An on-site test by an aircraft maintenance engineer (AME) involved blowing into the pitot and static ports: the pitot port was clear, but the static port was blocked, with no air exiting the other end. The pitot-static system and Mode C transponder had been tested on 19 April 2021, and the most recent Mandatory Periodic Inspection (MPI) on 22 June 2021 found the pitot and static systems serviceable. The aircraft flew an additional 84 hours until the incident.
Findings and Probable Cause
The investigation noted that the static port blockage likely went unrecognized until the descent, consistent with FAA guidance on partial static system blockage. During descent, the airspeed indicator showed erroneously high readings, and during climb, it decreased rapidly. The pilot continued operations while the aircraft exceeded its never-exceed speed (Vne) of 155 knots.
Probable cause: "It is probable that whilst flying over the mountain range, the aircraft experienced a downdraft which caused the aircraft to start descending. With the static port blocked, the airspeed indicator began to give inaccurate readings which the pilot interpreted as actual."
Contributory factor: "The pilot initiated a precautionary landing and during the landing roll, the aircraft’s wings were caught in a wire fence."
Meteorological Information
At the time of the incident, the METAR for FARG at 1400Z reported wind 060°/2 knots, temperature 22°C, dew point 3°C, and QNH 1026 hPa. The aircraft was flying west, encountering a tailwind over the mountains.
No safety actions were taken by the involved parties. The report recommends that pilots be made aware, through training, of possible in-flight signs of pitot system failure.