What happened
On 20 October 2006, a Glos-Airtourer Super 150, registration G-AZHI, was engaged in a private flight for the purpose of practicing aerobatic manoeuvres. While the aircraft was levelled at 3,000 ft with an airspeed of approximately 120 kt, the upper right engine cowl became unlatched. The component began to oscillate violently between the fully open and fully closed positions.
In response to the instability, the pilot immediately reduced engine power and raised the aircraft's nose to decrease airspeed. Within approximately five seconds, the cowl detached from the aircraft, striking the windscreen before disappearing from view. The pilot declared an emergency via radio and successfully returned to the departure airfield to land. The incident resulted in no injuries, though the aircraft sustained damage, including a missing starboard upper engine cowl, a scratched windscreen, and punctures to the elevator skin and the leading edge of the tailplane.
The investigation
Following the event, the aircraft and the detached cowl were inspected by a licensed aircraft engineer. The investigation focused on the securing mechanisms of the engine cowls. The engineer examined the three over-centre latches and their corresponding receivers but found no evidence of distress, damage, or failure in these components. It was noted that the aircraft was scheduled for maintenance two weeks after the accident, which included an intended upgrade to the upper engine cowl fasteners.