Contaminated Runway Go/No-Go
You command a twin-engine turboprop with a planned take-off mass of 5,400 kg and MTOM 5,700 kg. Runway 08 at a northern Norwegian airport has TORA/TODA 1,400 m, elevation 30 m, and a 1.0% uphill slope. QNH is 1000 hPa, OAT is −5 °C, and the wind is 080° at 12 kt. The runway is covered by 5 mm of wet snow; braking action is reported medium to poor, and the runway has not been ploughed. The AFM contaminated-runway supplement for wet snow gives a take-off distance factor of 1.30 and permits a maximum of 5 mm. The dry, sea-level, ISA, zero-wind, level baseline take-off distance at 5,400 kg is 1,050 m. Apply an uphill slope correction of +5%, a headwind correction of −10% per 10 kt, and a cold-temperature correction of −3%. The accelerate-stop distance on the contaminated surface is 1,360 m. Your slot is in 20 minutes and the destination forecast is improving.
1. Calculate the corrected take-off distance required and compare it with the available distance.
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Apply corrections in sequence to the baseline 1,050 m:
- Wet snow: 1,050 × 1.30 = 1,365 m
- Uphill slope: 1,365 × 1.05 = 1,433 m
- Headwind 12 kt: 12/10 × 10% = 12% reduction; 1,433 × 0.88 = 1,261 m
- Cold temperature: 1,261 × 0.97 = 1,223 m
Corrected TODR is about 1,223 m against TODA 1,400 m, a margin of 177 m. However, the contaminated accelerate-stop distance is 1,360 m against 1,400 m, only 40 m (2.9%) margin. The distance calculation alone does not make the departure operationally sound.
2. Is the departure acceptable? Justify with operational reasoning and state what you would do.
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I would not accept the departure without addressing the contamination. The AFM limit is exactly 5 mm, so any drift or unmeasured patch invalidates the calculation. Braking action medium to poor and an unploughed runway make a high-energy rejected take-off critical with only 40 m ASDA margin. Slot pressure is not a safety factor. Options: wait for ploughing and a new braking report, reduce mass to improve both TODR and ASDA, or delay. If departing after improvement, brief a rejected take-off, use full reverse and maximum braking, verify actual snow depth, recalculate V1/VR, and set a personal stop if braking is worse than reported. The destination improving does not offset the departure risk.