AAIB Bulletin No: 4/2003 Ref: EW/G2002/11/07

facial burns but his passenger received serious burns to his face and hands. The fire service arrived at the scene within five minutes and extinguished a smouldering fire. Weather The wind was very light at the time of departure. The METAR for Leeds/Bradford Airport, 37 nm north-west of Netherthorpe, reported a wind of 1 kt from 360 degrees, 10 minutes prior to the accident and the same wind 20 minutes after the accident. The METAR for East Midlands airport 30 nm south of Netherthorpe reported a wind of 0 kt, 10 minutes prior to the accident and the same wind 20 minutes after the accident. The approximate temperature and dewpoint in the Netherthorpe area at the time of the accident were 9°C and 5°C respectively and the mean sea level pressure was 1008 mb (QNH). The total rainfall for the Netherthorpe area in the previous nine days including the day of the accident was 43.8 mm. The total rainfall the day before the accident was 8.7 mm and an additional 7.4 mm of rain fell on the day of the accident. Take-off Distance Calculation The Tomahawk flight manual contains a chart showing the take-off distance to a height of 50 feet assuming the following: one notch of flaps, lift off speed 53 KIAS, full power before brake release, paved level dry runway, and maximum take-off weight of 1,670 lb. Assuming zero wind, a temperature of 9°C and a pressure altitude of 400 feet (Netherthorpe conditions at the time of the accident) the published take-off distance to a height of 50 feet is 1,300 feet which equals 396 metres. The flight manual contains a CAA change sheet that requires that the reported take-off distance figures be factored by 1.05 because flight tests established that the Tomahawk failed to achieve the reported performance. Therefore, the actual take-off distance to 50 feet is (396) x (1.05) = 416 metres. This figure assumes a dry level paved runway. Runway 24 at Netherthorpe was damp, sloped uphill and had a grass surface. The flight manual does not provide correction factors for these conditions but the CAA Safety Sense Leaflet 7B Aeroplane Performance does provide factors. The following factors in the Safety Sense Leaflet are to be multiplied by the take-off distance to a height of 50 feet: Condition Factor A 2% uphill slope 1.1 Dry grass 1.2 Wet grass 1.3 Additional Safety Factor 1.33 Runway 24 at Netherthorpe had a 1.9% uphill slope and therefore a factor of 1.095 is appropriate. The grass runway was described as damp and therefore a factor of 1.25, which is halfway between the dry grass factor and the wet grass factor, could be reasonably assumed. The CAAs 1.33 safety factor is designed to account for variations in take-off technique and a reduction in performance compared to published figures due to wear and tear on the aircraft and engine. If a flight manual does not already include approved factored data, then the 1.33 safety factor should be applied. Applying these three factors to the take-off distance results in: (416 metres) x 1.095 x 1.25 x 1.33 = 757 metres This figure is the estimated take-off distance required to achieve a height of 50 feet given the conditions at the time of the accident. The Aeronautical Information Publication (AIP) does not publish a TODA (Take-Off Distance Available) figure for Netherthorpe airfield. TODA is the sum of the useable runway length plus any clearway. A clearway is an area beyond the end of the runway which is clear of significant vertical obstacles; this area is always wider than the runway. The AIP entry reports a TORA (Take-Off Run Available which means the useable length of runway) of 490 metres and states that the total length of the grass strip is 553 metres. Since there is a road and a hedge at the end of Runway 24, the take- off distance required of 757 metres significantly exceeded the take-off distance available. The pilot performed a take-off distance calculation prior to departure. He applied a 1.1 factor for the uphill slope, a 1.2 factor for the grass surface and a 1.33 safety factor. However, he mistakenly applied these factors to the take-off ground roll distance in the flight manual rather than the take-off distance to a height of 50 feet. The take-off ground roll distance he used was 213 metres and applying the 1.1, 1.2 and 1.33 factors gave him a 375 metres take-off ground run distance which is less than the TORA of 490m. In addition, the pilot assumed a 5 kt headwind in his calculations; he assumed a dry runway and he did not apply the 1.05 factor required by the CAA change sheet. The CAA safety sense leaflet on take-off performance only provides factors for calculating take-off distance required and does not provide factors for directly calculating take-off ground run required. The leaflet includes a note, referring to the factors for dry grass, wet grass and 2% slope, which states: Effect on Ground Run/Roll will be greater. Discussion Given the aircrafts performance, its weight, the weather and the runway surface conditions at the time, there was insufficient runway length available for the aircraft to become safely airborne. In his report the pilot was very honest and admitted that he had underestimated the take-off distance required in his calculations. He had on a previous occasion departed safely from Netherthorpe airfield in the same aircraft on his own and that may have affected his confidence. In addition, witnessing four aircraft departing safely in front of him also convinced him that the conditions did not present a problem. He also stated that he made a mistake in not aborting the takeoff at the halfway point when it was first apparent that the aircraft was not accelerating sufficiently. The CAA does not publish correction factors for calculating the take-off ground run required. The factors in Safety Sense Leaflet 7B must be applied to the take-off distance to a height of 50 feet. The same factors and guidelines are also included in Aeronautical Information Circular AIC 67/2002. AIC 67/2002 states: The pilot should always ensure that, after applying all the relevant factors including the safety factor, the take-off distance to a height of 50 feet (TODR) does not exceed the runway length available (or TODA if known). The TODR in this case was 757 metres and the total published runway length was 553 metres.