Descent into Kuala Belait with a Sea Breeze and a Runway Crosswind Limit
You are descending into Kuala Belait (a coastal aerodrome in Brunei) at 1500 ft on a hot afternoon. The runway is 04/22, 1200 m long, and the aircraft's crosswind limit is 15 kt. The 1400 METAR reads: wind 270/14 kt, visibility 10 km, FEW020, temperature 33°C, dewpoint 26°C, QNH 1009. The TAF expects the sea breeze to strengthen to 18 kt by 1600. The aerodrome has a 10 m elevation and a 3° glideslope. Your aircraft's landing distance required at 33°C is 950 m.
1. Calculate the crosswind component for runway 04 and runway 22 and decide which runway to use, given the crosswind limit and the forecast trend.
Read the worked answer
Runway 04 is oriented 040°, runway 22 is 220°. The wind is 270° at 14 kt. The angle between wind and runway 04 is 230°, so the crosswind component is 14 × sin(230°) = 14 × 0.766 = 10.7 kt. The headwind component on 04 is 14 × cos(230°) = -9.0 kt, i.e., a 9 kt tailwind. On runway 22 the angle is 50°, so the crosswind is 14 × sin(50°) = 10.7 kt and the headwind is 14 × cos(50°) = 9.0 kt. Both runways are within the 15 kt crosswind limit, but runway 04 gives a 9 kt tailwind, which increases landing distance and is undesirable at 33°C. Runway 22 gives a 9 kt headwind and a 10.7 kt crosswind, so use runway 22. If the sea breeze strengthens to 18 kt, the crosswind on 22 becomes 18 × sin(50°) = 13.8 kt, still within the 15 kt limit but close. Monitor the trend and be prepared to divert if it exceeds 15 kt.
2. Assess the effect of temperature and density on the landing distance and decide whether the 1200 m runway is adequate.
Read the worked answer
At 33°C and QNH 1009, the density altitude is higher than the aerodrome elevation of 10 m. Using the approximation that density altitude rises about 120 ft per 1°C above ISA at sea level, the ISA temperature at 10 m is about 15°C, so the excess is 18°C, giving a density altitude of roughly 10 + 18 × 120 = 2170 ft. The landing distance required of 950 m is for the actual conditions, but if it is a sea-level ISA figure, it must be increased for density altitude. A 10% increase per 1000 ft of density altitude gives about 22%, so the required distance becomes about 1160 m. The 1200 m runway leaves only 40 m of margin, which is inadequate for a commercial operation. Use the manufacturer's landing chart for the actual weight, temperature, and QNH, and if the required distance exceeds the available runway, divert to a longer runway or wait for cooler conditions.