What happened
On 21 July 2019, a Midget Mustang, registration G-AWIR, was conducting a private flight from Leicester Airfield to Sibson Airfield. During the flight, the pilot flew over Spanhoe Airfield at an altitude of approximately 600 to 700 feet to observe the windsock and determine if a landing was appropriate for a visit to friends.
Following this observation, the pilot initiated a pull-up and a left bank. During this manoeuvre, the aircraft departed controlled flight and descended into a wooded area near the airfield. The impact resulted in serious injuries to the pilot and the destruction of the aircraft.
The investigation
The investigation focused on the aerodynamic changes occurring during the pilot's manoeuvre. Investigators examined the relationship between load factor, bank angle, and stall speed. It was noted that as an aircraft banks, the lift vector is no longer directed solely against gravity, requiring an increase in lift to maintain altitude. This increase in lift raises the load factor, which in turn increases the aircraft's stall speed.
For the Midget Mustang, the published stall speed in a clean configuration at maximum gross weight is 60 mph. The investigation considered how the combination of a pull-up and a steep bank would significantly raise the stalling speed while simultaneously reducing airspeed due to increased drag and the loss of vertical lift component.