What happened
On 9 January 2022, a CAP 231, registration G-IIHZ, was conducting a private aerobatic display practice flight near the North Norfolk coast. The pilot had departed from Northrepps Airfield and was performing a series of high-energy manoeuvres. During a vertical left roll, the pilot experienced a sudden jolt through the airframe, which immediately caused the aircraft to depart into an inverted spin.
Upon realising that the yaw control was behaving abnormally, the pilot reduced throttle and used the ailerons to recover the aircraft to level flight. The pilot subsequently performed an extended approach and landed safely back at Northrepps Airfield. There were no injuries to the pilot during the occurrence.
The investigation
An inspection of the aircraft following the flight revealed significant damage to the tail section. The rudder control horn had partially broken away from the rudder structure on the left side, and the aluminium alloy fairing at the bottom leading edge of the rudder was found to be trapped and deformed. Furthermore, the stern post of the fin had dis-bonded from the fin structure.
Investigators examined the wooden construction of the rudder and fin, noting that the rudder consists of plywood skins and ribs covered in fabric and epoxy. The investigation focused on the lower hinge assembly and the attachment points of the stern post. Evidence was found that a previous repair had been made to the attachment of the stern post to the fin skins, and the glue bead on the right side of this repair appeared insufficient.