Shamal Dust and Gust Crosswind
At 1200 UTC in mid-July you are preparing to depart Kuwait International (elevation 63 m) in a twin turboprop. METAR OKBK 121200Z 02020G36KT 3000 BLDU SCT040 44/08 Q0998. The TAF for 1200–1400 UTC includes TEMPO 02025G45KT 1500 BLDU. Runway 33L (330°) is in use; TORA is 3,400 m. Your aircraft has a demonstrated crosswind limit of 25 kt and an operator takeoff minimum of 800 m visibility. The AFM takeoff distance at 5,200 kg, pressure altitude 500 ft and 45°C is 2,620 m on a dry runway. The first officer says the wind is 'mostly down the runway' and wants to depart before the dust worsens. The aircraft is loaded to 5,200 kg. There is no takeoff alternate available, and the destination forecast is not relevant for this local departure.
1. Calculate the steady and gust crosswind and headwind components for runway 33L. Compare them with the aircraft limit.
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The wind is 020° and the runway is 330°, so the angle between them is 50°.
Crosswind = wind speed × sin 50°:
- steady: 20 × 0.766 = 15.3 kt
- gust: 36 × 0.766 = 27.6 kt
- TEMPO gust: 45 × 0.766 = 34.5 kt
Headwind = wind speed × cos 50°:
- steady: 20 × 0.643 = 12.9 kt
- gust: 36 × 0.643 = 23.1 kt
The steady crosswind is below 25 kt, but the current gust component 27.6 kt already exceeds the aircraft crosswind limit, and the TEMPO condition reaches 34.5 kt. The first officer's 'mostly down the runway' is wrong: the wind is 50° off the runway centreline.
2. Using the visibility, TAF and takeoff performance data, decide whether to depart now. Explain the limiting factor and what you would do next.
Read the worked answer
Visibility is 3,000 m in blowing dust, above the operator minimum of 800 m. The TEMPO visibility of 1,500 m is also above 800 m, although it shows deterioration. Takeoff performance is not limiting: pressure altitude is 63 + (1013 − 998) × 30 = 513 ft, close to the 500 ft AFM figure, and the 2,620 m dry-runway distance is well within the 3,400 m TORA; the headwind component would reduce it further.
The limiting factor is crosswind. The gust crosswind of 27.6 kt exceeds the 25 kt limit, so a departure now is not acceptable. I would hold the aircraft, keep passengers informed, and monitor the METAR/TAF for the gust to decrease. Because both parallel runways have the same orientation, changing runway does not solve a 50° crosswind; waiting is the practical option. I would also consider the dust trend and the possibility of a return if visibility drops toward the operator minimum.