Landing at Labuan - Contaminated Runway and Factored Distance
You are landing a twin turboprop (MLW 8,600 kg) at Labuan (elevation 100 ft, QNH 1010, OAT 30 °C) on Runway 14, LDA 2,300 m. The runway has 3 mm of standing water and reported braking action is medium. The AFM landing chart (dry, sea level, ISA, zero wind, no slope) gives a landing distance of 1,050 m at MLW. The operator's contaminated-runway supplement says to multiply the dry landing distance by 1.92 for 3 mm of water with medium braking. Wind is 140°/12 kt. The runway has a 0.3 % downhill slope. Company SOP requires landing within 60 % of LDA on a contaminated runway.
1. Calculate the factored landing distance and determine whether the landing is acceptable under the SOP.
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Start with the AFM dry landing distance at MLW: 1,050 m. Apply the contaminated-runway multiplier of 1.92: 1,050 × 1.92 = 2,016 m.
Apply wind: 12 kt headwind, essentially aligned. Using a 50 % factor for the headwind and a typical 1.5 % reduction per knot of effective headwind, 6 kt effective gives about 9 % reduction: 2,016 × 0.91 ≈ 1,835 m. Apply the 0.3 % downhill slope: landing distance increases about 5 % per 1 % downhill, so add 1.5 %: 1,835 × 1.015 ≈ 1,863 m.
Compare with the SOP limit of 60 % of LDA: 0.60 × 2,300 = 1,380 m. The factored distance of 1,863 m far exceeds 1,380 m, so the landing is not acceptable under the SOP.
The remedy is to reduce landing mass until the factored distance falls within 1,380 m, which requires roughly a 26 % reduction in the dry chart value, or to wait for the water to drain and braking action to improve to good. Do not accept the landing on the basis that 1,863 m is less than the 2,300 m LDA; the SOP margin is the governing criterion.
2. Explain why the 60 % SOP criterion is more demanding than the certification requirement and what it protects against.
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Certification landing distances are demonstrated on a dry runway by a test pilot, at a known mass, with a steady approach, immediate braking and no reverse thrust credit in many cases. They represent a best-case, not an average-case, outcome. The 60 % criterion builds in a margin for pilot technique, late braking, runway contamination variability, wind shear, and the fact that the reported braking action is an average over the runway, not a guarantee at every point.
The 60 % figure also protects against the situation where the aeroplane touches down long. On a 2,300 m runway with 1,863 m of factored distance, a 400 m long landing would leave almost no stopping margin. The SOP margin ensures that even a mediocre approach and touchdown still leaves runway ahead.
Finally, the criterion is a planning tool, not a guarantee: if the actual braking action on touchdown is worse than reported, the pilot must be prepared to go around. The decision to land should be made before descending below the approach ban, using the calculated figures, not adjusted in the flare.