What happened
On 28 February 2013, a Diamond Aircraft DA 40D, registration SE-MBC, was taxiing at Borliente Airport, Sweden, for a flight to Västerås. The taxiing process lasted approximately five minutes and covered a distance of 2,100 meters. During this period, the aircraft was operating in a significant 21-knot tailwind.
As the pilot attempted to maintain a straight path on the runway, the aircraft's direction was influenced by several competing forces. The clockwise rotation of the propeller created a leftward moment, while the tailwind caused the rudder to produce an inverse steering effect. To counteract these forces and keep the aircraft on the runway, the pilot relied heavily on the right brake, making several stops along the route.
Upon reaching the end of the runway, the pilot observed smoke emanating from the right side of the aircraft and notified the tower. The pilot subsequently evacuated the aircraft via the canopy. Although a technician attempted to use a handheld extinguisher, the fire spread from the right wheel to the inner part of the right wing and the flap, causing substantial damage to the aircraft.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the mechanical and aerodynamic factors contributing to the event. The investigation focused on the interaction between the aircraft's steering systems and the environmental conditions. Because the nose wheel on this model is free-castering and not directly linked to the pedals, the pilot had to use differential braking to steer.
The investigators analyzed how the engine power required to maintain thrust, combined with the aerodynamic moments from the propeller and the tailwind, necessitated intense braking. They also looked into the role of the composite wheel fairings, which helped trap heat near the brake assembly.
Findings
- The aircraft was operating in a 21-knot tailwind.
- The pilot used the right brake extensively to maintain the runway heading.
- The combination of engine thrust, propeller-induced moments, and rudder effects required continuous braking pressure.
- The risk of the brakes overheating on this aircraft type was not evaluated in an appropriate manner.
- At the time of the accident, the Aircraft Flight Manual (AFM) did not contain specific warnings regarding the risk of brake overheating during prolonged taxiing in such conditions.