What happened
On 27 January 2004, a Sirocco 377GB, registration G-MNDW, was conducting a private flight near Derby Airfield. The pilot, an experienced aviator with nearly 9,500 flying hours, had recently acquired the aircraft. After performing routine flight manoeuvres, the aircraft was observed by witnesses near Ashby-de-la-Zouch.
While flying in a north-westerly direction, the aircraft suddenly banked sharply to the left. Witnesses reported seeing parts of the wing appear to bend upwards before the aircraft entered a rapid, steep spiral towards the ground. The impact was severe, and the pilot sustained 1 fatal injury. There was no post-crash fire, and the aircraft was destroyed.
The investigation
The AAIB investigation focused on the structural integrity of the aircraft's tailplane. Although the aircraft had undergone mandatory modifications intended to prevent tailplane failure—following a similar fatal accident in 1995—the investigation found that the tailplane had failed in a nearly identical manner.
Examination of the wreckage revealed that the tailplane had essentially shaken itself apart. The internal components, including the foam ribs and the spar, had separated from the outer skins. Investigators also noted that the aircraft was using retaining pins rather than the required bolts and wing nuts for the tailplane attachment. Furthermore, scientific analysis by QinetiQ identified significant manufacturing and modification defects, including poor adhesive bonding and evidence that moisture had been trapped within the tailplane structure, potentially degrading the wooden components.
Findings
- The primary cause of the accident was an in-flight structural failure of the tailplane due to aerodynamic flutter.
- The tailplane's structural integrity was compromised by poor adhesive bonding between the skins, ribs, and spar, present both from original manufacture and during the application of previous modifications.
- The lack of drainage holes allowed moisture to accumulate within the tailplane, leading to the degradation of the wooden locating ribs.
- The aircraft lacked the mass balance modification recommended by the original manufacturer to mitigate flutter risks.
- The use of retaining pins instead of bolts increased the likelihood of instability in the tailplane mounting.