What happened
On 16 April 2023, a Pierre Robin R2160, registration G-BLWY, was conducting an aerobatic training flight over open countryside. While the pilot was performing a clearing turn at approximately 100 kt with a 60-degree bank angle, a transparent panel covering the rear section of the cockpit detached and fell from the aircraft. Following the incident, the pilot successfully returned the aircraft to Deeneth to land at Deenethorpe Airfield. There were no injuries to the two occupants, though the aircraft sustained minor damage to the right wing, flap, and rear fuselage.
The investigation
Investigators examined the structure of the cockpit's transparent panels, which are secured to the fuselage and a central ridge frame using a combination of sealing adhesive, screws, and a capping strip. The investigation revealed that the panel had broken into jagged pieces, which remained trapped under the existing screws and adhesive.
Crucially, the leading edge of the panel, where it meets the hoop frame located behind the seats, had completely disbonded from the structure. This separation also involved the loss of parts of the canopy weather seal. When inspecting the left-hand panel, investigators found that the adhesive bond along the hoop frame was already beginning to fail, as the material could be lifted with finger pressure.
Findings
- The primary cause of the panel's detachment was the failure of the adhesive bond at the leading edge of the panel where it attaches to the hoop frame.
- Once the bond failed, airflow was able to penetrate the gap between the frame and the panel, creating enough upward force to break the material.
- The panel is constructed from polymethyl methacrylate (PMMA), a material that is susceptible to cracking when subjected to loads that cause flexing or distortion from its original shape.