Wet or Contaminated Take-off with a Valid Load Sheet
You are captain of a Boeing 737-800 departing Runway 18 at an airport with elevation 1,250 ft and runway slope +0.8%. TORA 2,600 m, TODA 2,600 m, ASDA 2,450 m. Take-off mass is 66,800 kg, OAT 30°C, QNH 1004 hPa, wind 180/12 kt. You plan TOGA thrust, packs on, engine anti-ice off. The AFM/QRH corrected figures for these conditions give maximum take-off mass 68,300 kg dry, 66,100 kg wet, and 63,900 kg with 5 mm standing water. Dry V1/VR/V2 are 148/150/156 kt; wet-runway V1 must not exceed 143 kt. After lining up, you see continuous water about 5 mm deep in the middle third, and the preceding aircraft reports medium braking action. The dispatcher says the load sheet was computed for wet runway and is still valid. The first officer suggests continuing because we can always stop before V1.
1. Using the figures given, determine whether the take-off may proceed and identify the controlling limit. Show the mass comparison and explain why the dispatcher's statement is not sufficient.
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Actual mass is 66,800 kg. Against the dry limit of 68,300 kg it is acceptable; against the wet limit of 66,100 kg it exceeds by 700 kg; against the 5 mm standing-water limit of 63,900 kg it exceeds by 2,900 kg. The observed contaminant is 5 mm water, so the wet-runway load sheet is not valid for the actual condition. The controlling limit is the contaminated-runway field/stop limit, not the dry field limit. ASDA 2,450 m is shorter than TORA, so V1 is stop-distance-limited; the wet V1 cap of 143 kt is an additional constraint. There is no clearway, so TODA gives no relief. Legal options are to reduce take-off mass to 63,900 kg or less, use a dry runway, or wait for the water to clear and recompute. The dispatcher's statement does not override the observed runway condition.
2. Assume you reject the take-off at 130 kt with about 1,800 m of runway remaining. What factors determine whether a stop is achievable, and what would you do?
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At 130 kt the aircraft is below the planned wet V1 of 143 kt, so a reject is still permitted in principle. The decision must be based on the contaminated stopping distance from 130 kt, not on the dry distance. With 1,800 m remaining, use the AFM contaminated stop data and any crew factor; if the required stop distance exceeds 1,800 m, do not reject - continue, fly, and deal with the problem airborne. If stopping is assured, close thrust, select maximum braking and spoilers, use reverse thrust, and maintain directional control; expect poor or asymmetric braking and possible hydroplaning. Do not delay the decision: a late reject at high speed on water is more dangerous than continuing. After stopping, inspect brakes and hot brakes.
3. If the operator decides to wait for the water to drain, what performance and V-speed changes must be rechecked before departure?
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The crew must recheck the actual contaminant depth and braking action, not just the word wet. Recompute take-off mass against the dry, wet or contaminated limits as applicable. Recheck V1 against ASDA and the wet or contaminated cap, and recheck VR/V2, field length, obstacle and tyre/brake limits. Use TOGA thrust; no assumed temperature. Confirm wind, OAT, QNH and runway slope. If the runway becomes merely wet, mass must be at or below 66,100 kg; if dry, 68,300 kg. Also confirm the take-off alternate and weather. A new load sheet and performance calculation are required before departure.