What happened
On 9 November 2002, a Ventus-2CT glider, registration ZS-GUW, was being aerotowed from Orient Aerodrome by a Piper Super Cub, registration ZS-EGI. During the climb phase, the aircraft was performing a safety circuit at approximately 450 feet above ground level. Amidst turbulent conditions, the glider pilot notified the tug pilot that the glider was out of position. Shortly thereafter, the pilot released the tow cable. Following the release, the glider initiated a left-hand turn, but the aircraft quickly entered a left-hand spin. The glider dived nose-first into the ground, resulting in the 1 fatality of the pilot and the total destruction of the aircraft.
The investigation
SACAA AIID investigators examined the flight logger data and interviewed witnesses to reconstruct the flight path. The investigation focused on the airspeed and altitude of the aircraft during the critical moments of the climb and the subsequent turn. Witnesses at the airfield observed the glider's erratic movement, noting that the aircraft appeared to roll inverted and plunge toward the terrain. The investigation also included flight testing of a similar Ventus-2CT model to understand the aerodynamic characteristics of the aircraft during low-speed, high-load maneuvers.
Findings
- The glider was flying at an airspeed as low as 64 mph, which was below the ideal range of 75–80 mph for an aircraft carrying full water ballast.
- The pilot released the tow cable before reaching the intended altitude because the aircraft had lost its position behind the tug.
- After the release, the pilot attempted to climb using what appeared to be rising air, but the flight logger indicated the aircraft actually encountered sinking air (negative lift).
- As the pilot tightened the left-hand turn, the airspeed dropped further to 67 mph, causing the left wing to stall.
- The resulting left-hand spin was so violent and rapid that the aircraft rolled inverted within approximately 1.5 seconds, leaving no opportunity for recovery at such a low altitude.
- The aircraft and its components were found to be in a serviceable condition prior to the accident, with no mechanical failures identified.