Air Accidents Investigation Branch
Summary:
During an aerobatic practice flight, G-BOXV was seen to enter a climbing vertical rolling manoeuvre from approximately 420 ft agl. The aircraft yawed right at the top of the manoeuvre which apexed at approximately 1,100 ft agl. During the right yaw, an uncommanded autorotative right roll developed and the aircraft entered a steep nose-down spiral dive. As the pilot attempted to pull out of the ensuing dive, the aircraft experienced an accelerated stall and a rolling departure to the right. At that point there was insufficient height remaining in which to effect a safe recovery and the aircraft struck the ground. The pilot was fatally injured in the accident.
No causal or contributory technical issues were identified during the post-accident examination of the aircraft.
The investigation found that the entry conditions to the initial climbing manoeuvre gave little or no safety margin when the aircraft began to dynamically diverge from the expected flight path at the apex. Entering the manoeuvre with more height and/or speed would likely have increased the pilots chances of avoiding the loss of control and/or being able to recover from it safely.
Generic guidance for aerobatic pilots is contained in CAA Safety Sense Leaflet 19 Aerobatics.