A Nomad N24A, powered by 2 Allison 250-B17 turboprop engines, was operating out of Royal Air Force airbase Weston-on-the-Green for parachute jumps. The weather was good, wind 360º/15kt, the temperature was 15ºC, visibility was 30 km, and some stratocumulus clouds were around with a base of 3000 feet. A first flight was completed successfully and 12 parachutists had jumped out of the aircraft at 12.000 feet. This first flight used 144 lb of fuel.
The aircraft in its final position after the aborted take-off (© Steven Coe)
A second flight was to be performed with 13 parachutists. As the aircraft taxied to the (grass) runway 01 (3194 feet take-off length), and the take-off clearance was received, the pilot checked the condition levers were set to 100% N2, Flaps were set at 10º and the trim was in the take-off range. Engine parameters were checked as well to match the company's recommended power setting.
Turbine Outlet Temperature @ 738ºC & Manifold pressure 89 psi. The maximum take-off power available (maximum 5 minutes) was Turbine Outlet Temperature @ 810ºC & Manifold pressure 102 psi.
The aircraft being parted out (© Erik Frikke)
As the aircraft reached a speed just above 80 knots (well past the schedule Vr of 71 knots) the pilot initiated rotating the aircraft. He immediately felt that the aircraft felt nose-heavy, the nose did not lift off the runway and the acceleration had stopped. The take was aborted by;
Applying the brakes
Selecting the condition levers to full reverse.
While the aircraft decelerated the pilot turned the aircraft to the right, to avoid trees and bushes ahead of the aircraft. The aircraft hit an small earth mount with the speed between 15 and 20 knots, bringing it to an immediate stop. The pilot shut down the engines and selected fuel and batteries to off. All onboard the aircraft evacuated the aircraft and no injuries were reported.
The tail section in the waste bin (©Erik Frikke)
The aircraft was damaged beyond repair.
The Air Accident Investigation Branch was alerted and they started an investigation into the possible cause of the accident. They concluded their report (available by clicking here) with the following analysis;
"The pilot had successfully completed a similar flight in the same aircraft, in benign meteorological conditions and the available evidence suggests that the aircraft was serviceable.
He reported that during the second take-off run 'the company recommended take-off power of 738°C TOT and 89 psi was set and achieved'. The take-off was therefore attempted with only 89 - 90% of the maximum power available. This would have had the effect of not only increasing the take-off distance but also the 'ASDR' to achieve a successful rejected take-off from a speed at or beyond normal rotation speed.
With the flap position and trim set correctly for take-off, the pilot attempted to rotate the aircraft between 80 to 83 kt, at least 9 kt above the scheduled rotation speed of 71 kt. If the aircraft loading had been within the limits of mass and CG prompt rotation of the aircraft should have occurred. This however did not happen and instead, the pilot felt the aircraft to be 'more nose-heavy than normal'. The exact mass and CG for this flight are uncertain. If the CG position was at the forward limit for the calculated mass, control column forces would have been high but not sufficiently high to prevent a successful takeoff. Extreme forces would only have been encountered if the aircraft's CG position was significantly in error.
It is therefore considered that for the second takeoff of the day the aircraft's CG was significantly forward of the forward CG limit."