What happened
On 14 November 2008, an Extra EA 300/L, registration G-ZEXL, was performing formation aerobatic training at Sywell Aerodrome, Northamptonshire. While the aircraft was executing a maximum energy manoeuvre, a section of the fuselage known as the 'turtle deck' became detached from the airframe.
As the aircraft performed a high-performance 'break' manoeuvre, the unsecured composite panel struck the cockpit canopy, causing the Perspex to shatter. The panel continued its trajectory, impacting the rear fuselage and the tail section, resulting in damage to the tailplane and rudder. The pilot, seated in the rear tandem position, was able to terminate the display immediately and perform a safe landing. There were no injuries to the crew.
The investigation
The investigation focused on the structural integrity of the fuselage following a recent 150-hour maintenance inspection. It was noted that the aircraft had completed six previous flights since the maintenance work, all of which involved low-energy manoeuvres and had passed all pre-flight inspections without noted defects.
Investigators examined the attachment points for the detached panel. A review of maintenance records and photographic evidence revealed that four screws intended to secure the front horizontal edge of the panel were missing. Photographic evidence taken during the fourth flight following the maintenance inspection showed the absence of these screws. The maintenance organisation noted that the correct procedure involves tightening screws to finger tight before final torquing, and that the flexibility of the panel might have masked the absence of screw heads during previous inspections.
Findings
- The primary cause of the incident was the detachment of an unsecured fuselage panel during high-energy flight.
- Four screws required to secure the front edge of the 'turtle deck' panel were missing.
- It is likely these screws were either not replaced following the 150-hour maintenance inspection or were removed at an undetermined time prior to the accident.
- The pilot's use of a full-coverage helmet likely prevented significant head injuries when the canopy shattered.