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Given the following information, what is the maximum allowable wind speed that can be accepted without exceeding the tailwind limit?

Maximum allowable tailwind component for landing: 10 kt
Planned runway: 05 047°M
Surface wind direction reported by ATIS: 210°
VAR: 17°E

• A
8 kt
• B
10 kt
• C
18 kt
• D
15 kt

Wind directions True or Magnetic?

Any written meteorological information written (TAF, METAR, SIGMET, etc) will be given in true direction.
Any information (ATIS, ATC) given to help pilot to line up the aircraft with runway for take-off or landing is magnetic, because runways directions are always magnetic.

The wind velocity is made of two components, one acting along the runway called the headwind component, and the other acting across the runway called the crosswind component.
It is possible to calculate the crosswind component taking the sine and the cosine of the relative bearing between the runway and the wind direction.

Head/Tail wind component = Wind Speed x cosine (Relative Bearing)

Crosswind component = Wind Speed x sine (Relative Bearing)

The maximum tailwind component is 10 kts, relative bearing between the runway and the wind direction 210º (M) - 047º (M) = 163º.

Máx. Wind speed = 10 / cosine (163º) = 10,5 kts

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• Austro Control