What happened
On the day of the accident, a formation of three microlight aircraft departed from Pikes Point Aerodrome, intending to fly to Raglan. The aircraft, a Pterodactyl Ascender registered as ZK-FKF, was positioned as the second aircraft in a loose formation. While the group was traversing the Manukau Harbour, flying parallel to the north shore, the aircraft experienced a sudden dutch roll followed by a nose-down pitch. During this sequence, the right wing failed at approximately one-third of its span, causing the aircraft to plummet into the water. The pilot sustained fatal injuries in the impact.
The investigation
Investigators examined the wreckage and compared the structural damage found on ZK-FKF to similar incidents involving other Pterodactyl Ascender microlights that had experienced mid-air breakups. The investigation also reviewed video footage from two previous accidents. This footage revealed a pattern where the wings would undergo intense fluttering following an uncommanded pitch-down motion, with these flutter forces ultimately causing the structural breakup.
Findings
Technical analysis determined that the aircraft suffered from insufficient pitch stability reserves when operating at the higher end of its permitted speed range. This instability, combined with various other deficiencies in control and structural design, created a condition prone to the catastrophic failure observed.
Safety action
Following the findings regarding the design deficiencies of the aircraft type, a recommendation was made to withdraw the Permit to Fly for this model.