What happened
On 9 November 2002, a Piper PA-3able-112 Tomahawk, registration G-BTOD, was attempting a departure from Runway 24 at Netherthorpe Airfield in Nottinghamshire. The aircraft, carrying one pilot and one passenger, was operating at approximately its maximum takeoff weight.
During the takeoff roll, the aircraft failed to accelerate to the necessary speed. The pilot noted that the airspeed was significantly lower than expected halfway down the runway but elected to continue the takeoff. Due to the low sun position, visibility of the runway end was compromised. The aircraft became airborne only 20 metres before a low hedge at the airfield boundary, grazing the obstacle in the process.
Faced with the prospect of encountering a taller hedge and a barn further ahead, the pilot attempted to land in a nearby field. However, the aircraft struck a hedge, crossed a road, and then breached a second, 7-foot-high hedge before coming to rest near a barn. The impact tore off the right wing and ruptured the right fuel tank, causing an immediate fire. Both occupants escaped the wreckage; the pilot sustained minor facial burns, while the passenger suffered serious burns to the face and hands.
The investigation
The investigation focused on the takeoff performance and the calculations used by the pilot. It was established that the runway surface was damp grass with a 1.9% upward gradient. While the pilot had performed a takeoff distance calculation, he had incorrectly applied safety and environmental factors to the takeoff ground roll distance rather than the takeoff distance to a height of 50 feet.
Furthermore, the pilot's calculations failed to account for the 1.05 performance correction factor required by CAA change sheets, and he had incorrectly assumed a dry runway and a 5-knot headwind. The investigation determined that the actual required takeoff distance to reach 50 feet under the prevailing conditions was approximately 757 metres, which significantly exceeded the available runway length of 553 metres.
Findings
- The primary cause of the accident was insufficient runway length to safely achieve takeoff performance given the aircraft's weight, the uphill gradient, and the damp grass surface.
- The pilot's takeoff distance calculation was erroneous because it applied environmental factors to the ground roll rather than the distance to 50 feet.
- The pilot failed to abort the takeoff when it became apparent that the aircraft was not accelerating sufficiently.
- Reduced visibility caused by the low sun hindered the pilot's ability to monitor the runway end.