Wet Runway, Tailwind and a Rejected Take-off
At a 2,000 ft pressure-altitude airport, runway 27 is 2,400 m long, wet, with a 1% upslope. OAT is 30°C, wind is 270°/10 kt (a 10 kt tailwind), and the aircraft mass is 62,000 kg. The AFM wet-runway take-off distance at 62,000 kg, zero wind, zero slope is 2,150 m. The AFM states: add 20% for a 10 kt tailwind; add 5% for each 1% upslope; a 1,000 kg mass reduction below 62,000 kg shortens the distance by 1.8%. The crew's V1 is 138 kt. The only alternatives are to wait for the wind to veer to 360°/10 kt or to offload payload. There is no clearway or stopway, and a 50 ft obstacle lies 2,520 m from the start of the take-off run.
1. Calculate the corrected wet-runway take-off distance. Is the take-off legal from the 2,400 m runway? If not, what approximate mass reduction is needed?
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Start with the AFM wet distance 2,150 m. Tailwind correction: 2,150 × 1.20 = 2,580 m. Upslope correction: 2,580 × 1.05 = 2,709 m. This exceeds the 2,400 m runway and the 2,520 m obstacle point, so the take-off is not legal. Required reduction = (2,709 − 2,400) / 2,709 = 11.4%. At 1.8% per 1,000 kg, the reduction is 11.4 / 1.8 = 6.3 t, so mass must be about 55.7 t or less. That is a large payload/fuel penalty; the crew should verify the AFM data, obstacle clearance and V1/VR/V2 before accepting it, and should first consider waiting for wind or a different runway.
2. The wind settles at 360°/10 kt. Runway 27 is still wet with the same upslope. Recalculate and decide.
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Runway 27 is 270°; wind 360° is 90° off, so the tailwind component is zero. Only the upslope correction applies: 2,150 × 1.05 = 2,258 m. That leaves 142 m margin on the 2,400 m runway and also clears the 2,520 m obstacle point. The 10 kt crosswind must be checked against the aircraft limit and the runway width, and V1/VR/V2 and obstacle performance must be recalculated for the new wind. If all are satisfactory, waiting is a better option than offloading 6.3 t. The crew must also confirm the actual wind, because a late shift back to a tailwind would invalidate the calculation.
3. At 80 kt during the take-off roll there is a loud bang and severe vibration. V1 is 138 kt. What is the correct decision and what factors matter?
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Below V1 the take-off should be rejected for a significant failure such as a bang with severe vibration, because the aircraft should be able to stop on the remaining runway. The captain should close the throttles, maintain directional control, use maximum braking and spoilers/reverse as available, and not attempt to fly. On a wet runway with a tailwind, stopping distance is degraded, so the decision must be made immediately and the stop must be monitored. If the same failure occurred after V1, the take-off would normally be continued and the failure handled in the air. After stopping, the crew must inspect the engine, advise ATC, and not attempt another take-off until the cause is found.