What happened
On 10 September 2007, a pilot conducted a local flight from the Crosswinds private aerodrome near Tarlton to evaluate the performance of a newly installed propeller. The flight was being conducted under clear weather conditions. During the flight, the pilot executed a maneuver required by the manufacturer's testing protocol, which involves entering a shallow dive and subsequently pulling the aircraft's nose upward to monitor climb performance. During this pull-up maneuver, the left wing's leading edge strut attachment plate failed. This structural failure caused the wings to collapse, sending the Thunderbird Mk iv, registration ZU-EOV, into a vertical spiral dive. The aircraft struck an open field adjacent to the aerodrome, where the impact and a subsequent fire resulted in one fatality and the total destruction of the aircraft.
The investigation
SACAA AIID investigators examined the wreckage and the flight sequence to determine the cause of the structural failure. The investigation established that the pilot was properly licensed with a valid medical certificate and that the aircraft had been maintained according to required standards. On-site analysis of the wreckage revealed that the attachment plate for the leading edge strut on the left wing had failed in tension. This failure occurred because the forces applied during the flight maneuver exceeded the design strength of the component. The investigation also noted that the aircraft was equipped with all necessary standard communication and navigational equipment, and there were no reported defects in the engine or propeller prior to the event.
Findings
- The primary cause of the accident was that the design strength of the left-hand wing leading edge strut attachment plate was exceeded.
- The failure of this specific component led to the immediate collapse of the wings.
- The aircraft's destruction was caused by both the force of the impact and the resulting post-crash fire.
- The pilot was unable to recover from the spiral dive following the structural failure.
Safety action
Following the structural failure of part number W09, the manufacturer released Service Bulletin SB DAC 001. This bulletin required the strengthening of the leading edge strut attachment plates on both the left and right wings by installing additional W09 plates. Additionally, there is a recommendation that the CCA mandate this service bulletin to ensure all operators implement the necessary structural reinforcements.