What happened
On 15 May 2004, a Zlin Z.37 A-2 Bumble Bee, registration G-KDLN, was prepared for a private flight from a grass airstrip in Exmoor, Devon. During the pre-flight phase, the pilot moved the aircraft by hand toward a starting area. During this process, the aircraft rolled backward into a wire fence. Because the elevator control lock was engaged, the underside of the elevator made contact with a wooden fence post.
After starting the engine, the pilot taxied the aircraft forward. While the pilot noted a small dent on the underside of the elevator during a secondary inspection, no further damage was identified, and the flight proceeded to Popham, Hampshire. During the flight, the pilot observed a slight sideslip in level flight but attributed this to his relative lack of familiarity with this specific airframe. After a stop at Popham and a subsequent refueling at Henstroge, the pilot discovered that the mass balance horn on the left elevator had been removed.
The investigation
The investigation established that while the aircraft was positioned against the fence, a wire had become trapped between the fixed tailplane and the elevator mass balance horn. As the aircraft taxied away, the tension in the fence caused the wire to snag and eventually tear the horn from the aircraft. The pilot's initial inspection was focused on a dent caused by the wooden post and did not include a full perimeter check of the tailplane. Furthermore, a visual inspection was not performed after the stop at Popham, which might have identified the missing component before the final leg of the flight.