What happened
On 18 September 2013, a Slingsby T67C Firefly, registration G-RAFG, was conducting a training flight near Wellesbourne Mountford Airfield in Warwickshire. The pilot was performing an aerobatic demonstration for a prospective student. While climbing to approximately 3,000 ft to prepare for an aileron roll, the cockpit canopy suddenly released. This caused the aircraft to pitch nose-up and experience a significant loss of airspeed.
The pilot managed to lower the nose and perform a safe low-level return to the airfield. Upon landing, it was observed that while the carbon fibre frame of the canopy remained attached to the aircraft, the Perspex bubble had been almost entirely destroyed. There were no injuries to the pilot or the passenger on board.
The investigation
Investigators examined the canopy latching mechanism, which utilizes two hooks operated by both internal and external levers. The mechanism relies on hooks engaging with pins located on the fixed windscreen arch. The investigation focused on the ability of the crew to verify that the hooks were properly seated.
It was noted that a 2001 Service Bulletin (SB 1s3) had been issued by Slingsby Aviation to improve the visibility of the latch engagement. This modification involved cutting away parts of the trim to allow for a clearer visual check of the hooks and pins. The aircraft, G-RAFG, had not yet incorporated this recommended modification.
Furthermore, the maintenance company responsible for recent repairs to the aircraft noted that they had adjusted the latches to accommodate a temporary replacement canopy used for a ferry flight. While they reported the mechanism appeared to function normally, they acknowledged the possibility that the latches might have been maladjusted.
Findings
- The cockpit canopy opened unexpectedly during a climb, leading to the destruction of the Perspex component.
- The aircraft had not implemented the recommended modifications from Service Bulletin 173, which would have made it easier to visually confirm the hooks were correctly engaged.
- The failure of the canopy to remain closed may have been caused by the lack of the recommended visual inspection modification or the maladjustment of the latching mechanism.