What happened
On 26 May 2017, a Beagle B1/21 aircraft, registration ZS-IGY, was participating in the first day of the Presidents Trophy Air Race. The flight departed from Springs Aerodrome with the intention of returning to the same location after passing through several turning points. After successfully reaching the first waypoint at Piet Retief, the crew decided to deviate from the planned track to the right to avoid mountainous terrain.
As the aircraft approached Tafelkop Mountain, the pilot attempted to climb over a saddle in the mountain range. However, as the aircraft reached the leeward side of the peak, it encountered severe atmospheric disturbances. The pilot observed a rapid decay in airspeed and a significant rate of descent. In an attempt to avoid the terrain, the pilot initiated a left turn into a valley, but the aircraft struck the side of the mountain. The impact destroyed the aircraft, though the door unlatched upon impact, allowing the occupants to escape.
The investigation
An investigation by the SACAA AIID established that the aircraft was mechanically sound and the engine was functioning normally throughout the flight. The aircraft was within its weight and balance limits and had been maintained according to regulatory requirements. The pilot held a valid Airline Transport Pilot Licence and a current medical certificate.
Investigators examined the meteorological conditions, noting that official forecasts had predicted strong winds from the west and southwest in the Wakkerstroom area. The investigation also reviewed the crew's decision-making process regarding altitude and route selection relative to the mountain's topography.
Findings
- The aircraft encountered strong downdraughts on the leeward side of the mountain caused by the prevailing southwest winds.
- The climb performance of the Beagle B121 was insufficient to overcome the downward air currents and maintain necessary altitude.
- The pilot's decision to fly over the mountain left an insufficient margin of safety, as the aircraft was at too low an altitude to clear the terrain effectively during the encounter with mountain wave turbulence.
- An attempted evasive maneuver to turn into a valley was unsuccessful because the pilot did not maintain adequate awareness of the mountain'1s contour to the left.
- The pilot sustained serious injuries, while the navigator sustained minor injuries.
Safety action
Following the accident, a safety message was noted regarding the reliance on cellular networks for emergency communication. While the pilot was able to contact air traffic control using a cell phone, investigators noted that network limitations in remote areas make such devices unreliable as a primary emergency tool. It is recommended that aircraft be equipped with a serviceable ELT and that pilots consider carrying a personal locator beacon (PLB).