What happened
On 24 June 2007, a winch-launched instructional flight involving a Grob Flugzeugbau Twin Astir glider ended in an accident at Uitenhage Aerodrome (FAUH) in the Eastern Cape. The flight was being conducted with a student in the front seat and an instructor in the rear seat under clear weather conditions.
During the takeoff roll, the student allowed the left wing to drop. The instructor attempted to intervene to correct the aircraft's attitude, but the intervention occurred too late to prevent a loss of control. Realizing the launch could not be completed safely, the instructor attempted to abort the operation by releasing the winch cable from the glider. However, the instructor was unable to release the cable on the first two attempts. By the time the third attempt succeeded, the glider had already begun to swing around, traveling backward against the direction of the takeoff. The aircraft subsequently crashed on the runway, resulting in serious injuries to the student.
The investigation
SACAA AIID examined the mechanics of the release system and the cockpit ergonomics of the ZS-GPZ. The investigation confirmed that the aircraft had been properly maintained and the pilot held a valid license and medical certificate. Investigators focused on why the instructor failed to release the cable immediately upon noticing the wing drop. The inquiry found that while the release mechanism itself had not failed, the high tension on the cable made it difficult to operate. Furthermore, the physical placement of the release mechanism in the rear seat of this specific model presented significant ergonomic challenges.
Findings
- The primary cause of the accident was the inaccessible position of the release mechanism for the instructor, which prevented timely corrective action.
- The instructor's attempt to abort the launch was delayed because the tension on the cable release mechanism was too high, causing the first two release attempts to fail.
- The physical layout of the rear cockpit makes the release mechanism difficult to reach for pilots standing 5' 10" or taller.
- The aircraft sustained extensive damage to the nose fairing, wing spars, and wing tips during the impact.
Safety action
To prevent similar occurrences, it is recommended that the manufacturer evaluate a height limitation for pilots operating this aircraft type or redesign the release mechanism to ensure better accessibility for taller occupants.