History of the Flight
On 25 June 2020 at 2010 UTC, the pilot of a Savannah VG (registration G-CGTV) was preparing for a local evening flight from his home farm strip to Beverley Airfield. The strip, approximately 220 m long, was dry cut-grass pasture with power lines at the eastern end and farm buildings to the north. After completing pre-flight checks, the pilot lined up on an easterly heading into a light wind.
With flaps set to 20° (normal takeoff configuration), he began the takeoff roll. About two-thirds of the way along the ground roll, the aircraft struck a bump, causing the pilot's knee to contact the flap lever. The lever moved from the 20° to the 40° position, deploying full flaps. The aircraft started climbing at very low speed and was close to stalling. To avoid a stall, the pilot lowered the nose while maintaining enough height to clear the power lines.
After clearing the power lines, the pilot felt the left wing starting to stall and applied left rudder while lowering the nose further. The aircraft veered left and struck a stack of hay bales approximately 10 m above the ground. It then struck the ground tail first before coming to rest. The pilot turned off the fuel and exited the aircraft with only minor injuries.
Flap System
The Savannah VG is equipped with full-span trailing edge flaperons with settings of 0°, 20°, or 40°. A lever on the cockpit floor between the pilot's legs operates them; a locking button on top engages with a detent for each setting. The Pilot's Operating Handbook (POH) states that with flaps 20°, the aircraft lifts off between 26 and 30 kt, and the takeoff distance required to clear a 50 ft obstacle is 228 m. The pilot had practiced a full-flap takeoff once before with an instructor. The POH notes: "The short take off procedure [Flaps 40°] is a very delicate manuver [sic]. It is suggested to practice it with an instructor before attempting it." The stall speed is 26 kt with flaps fully extended and 30 kt with flaps retracted. The pilot stated that in flight, extending flaps requires overcoming aerodynamic loads, but on the ground, the flaps will fully extend under their own weight.
Discussion
During the takeoff ground roll, as the aircraft approached flying speed, it struck a bump, and the pilot inadvertently moved the flap lever. No defect was found in the flap mechanism. Due to low aerodynamic loads, the flaps deployed to 40°, creating a sudden increase in lift and drag and reducing the stall speed. The manufacturer had highlighted in the POH that taking off with flaps 40° requires delicate handling, as lift-off and stall speeds are very similar. The pilot had practiced rejected takeoff maneuvers to the right and straight ahead, but not to the left. The sensation of a left-wing stall led the pilot to turn left, and he realized he would strike the hay bales or farm buildings.
The POH states that 228 m is needed to clear a 50 ft obstacle. The strip was about 220 m long, and the power lines were approximately 20 ft high. However, due to the orientation of the power lines, the takeoff run available decreased as the aircraft turned left after takeoff.
The aircraft was destroyed. The pilot sustained minor injuries.