What happened
On July 27, 2012, a pilot was conducting a recreational flight in a Flight Design CTSW ultralight aircraft, departing from Bad Wörishofen. After approximately one hour of flight, the pilot performed a figure-eight maneuver. During this period, a loud bang occurred, and the cockpit canopy shattered. The aircraft entered an uncontrolled state, which the pilot managed to stabilize, though the aircraft remained in a continuous descent.
Deciding on an emergency landing, the pilot shut down the engine and deployed the ballistic recovery system (parachute) at an altitude between 50 and 80 meters. The aircraft struck a meadow near Ingenried with significant force. The impact caused severe damage to the aircraft, including a broken nose gear, a broken pilot seat, and the separation of the left horizontal stabilizer, which was recovered 3 km away in a wooded area. The pilot sustained severe spinal injuries due to the seat breaking during the impact.
The investigation
The BFU examined the aircraft, the flight data, and the wreckage. The investigation included a specialized structural analysis by Cranfield University to examine the broken horizontal stabilizer. The investigators also reviewed the maintenance history and the manufacturer's production methods.
Technical analysis of the stabilizer revealed that the construction of the shear webs contained multiple stress concentrations. Furthermore, the bonding between the skin and the spar cap was found to be suboptimal, characterized by poor adhesive penetration and contamination. The use of aramid fabric, which is difficult to bond, was also noted as a factor that contributed to the vulnerability of the joint.
Findings
- The primary cause of the accident was the structural failure of the horizontal stabilizer due to an aerodynamic overload.
- The pilot was flying at speeds between 2/75 and 275 km/h, significantly exceeding the permitted maximum speed (Vne) of 225 km/h for this aircraft at the time.
- The failure was exacerbated by manufacturing defects, specifically inadequate bonding and poor quality assurance during the assembly of the stabilizer.
- The severity of the pilot's spinal injury was caused by the activation of the recovery system at an extremely low altitude (50–80 m), which left the aircraft in a swinging motion and resulted in a nearly horizontal impact.
- The structural integrity of the stabilizer was weakened by the use of aramid fabric and improper adhesive application.