What happened
On 10 October 2021, a Motor Glider Stemme S-12, registration ZT-GZG, departed from Bethlehem Airfield in the Free State Province. The pilot intended to land at El Mirador Airfield in KwaZulu-Natal. During the approach to Runway 06, the aircraft encountered atmospheric disturbances caused by a 10-knot southerly wind blowing over an adjacent ridge and valley. This wind caused the glider to lose altitude unexpectedly.
In an attempt to compensate for the sinking rate, the pilot shortened the downwind and base legs of the landing pattern. This resulted in an insufficient approach height to properly align with the runway centerline. Upon touchdown, the pilot could not maintain the correct heading, causing the aircraft to veer right across a soft, ploughed field. The aircraft came to a stop approximately 50 metres from the runway. The incident resulted in 0 fatalities and 0 injuries, though the aircraft sustained minor damage, including a bent right-side main landing gear and a damaged nose cone.
The investigation
The investigation examined the flight path, weather conditions, and the pilot's maneuvers. It was established that the pilot was operating under a valid Glider Pilot Licence and possessed a current medical certificate. The aircraft's maintenance records showed a recent inspection was completed earlier in the year. The investigation focused on the impact of local topography and wind patterns on the stability of the approach.
Findings
- The primary cause of the incident was an unstable approach that led to a loss of directional control during the landing roll.
- Local wind effects, specifically a 10-knot wind interacting with nearby terrain, caused the aircraft to sink.
- The pilot's decision to shorten the landing circuit legs to manage the sink rate prevented a stabilized approach to the runway.