What happened
On 14 March 2000, a North American T-6G Harvard, registration G-BKRA, was preparing for a one-hour type familiarisation flight at Leeds Bradford International Airport. The flight was intended for a student pilot, with the commander occupying the front seat and the student in the rear.
During the taxi phase, the aircraft was cleared to use Runway 32 and, if necessary, backtrack along Runway 14. The pilot opted to use the full length of the runway and began taxiing along Runway 14. At the time, wind conditions were stronger than predicted, with speeds between 20 and 30 knots and directions varying between 280° and 320°. To speed up the backtracking process, the pilot increased the taxi speed.
Shortly after accelerating, a significant tail wheel shimmy began. To prevent damage to the tail wheel unit, the pilot moved the control stick forward to a position slightly beyond neutral. This action caused the tail wheel to unlock and enter a free-castor state. Combined with the strong tailwind component, the aircraft immediately entered a right-hand ground loop, rotating through 270°.
The investigation
The investigation focused on the pilot's control inputs and the mechanical behavior of the tail wheel. The investigation examined the Flight Manual for the North American T-6G Harvard, which provides specific instructions for downwind taxiing. The manual states that the control stick should be held forward to prevent wind pressure from lifting the tail, but specifically warns that holding the stick full forward will unlock the tail wheel and allow it to swivel freely. To maintain steering engagement, the stick must be held a few inches behind the full forward position.
Findings
- The pilot moved the control stick too far forward, which unlocked the tail wheel.
- The unlocked tail wheel allowed the aircraft to lose directional control.
- High wind speeds and a significant tailwind component contributed to the severity of the ground loop.
- The pilot's decision to increase taxi speed to expedite the backtrack contributed to the onset of the shimmy and the subsequent loss of control.