In general -
Wind directions other than for a landing and take-off shall be expressed in degrees true.
Refernce is ICAO Annex 5 (Units of Measurament to be Used in Air and Ground Operations) Table 3-4 (Standard Application of specific units of measurament).
The only time wind direction is expressed in magnetic is when ATC tell you the wind for take-off or landing. Every other sourse gives the info in true.
To be specific -
ICAO Annex 3 (Meteorology) Appendix 4 Gives the requirements for Air Reports;
2.2 Wind Direction
Wind direction shall be reported in terms of degree true, rounded to the nearest whole degree.
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Now a question for you - do you upload winds to your FMS? If so do you correct every wind at every point for variation?
