Meteorology for Navigation
Pressure, wind and altimetry
The Meteorology for Navigation domain tests how weather changes aircraft performance, heading and altitude. QNH is the altimeter setting that makes the altimeter read elevation at the aerodrome; QFE makes it read height above the reference point. Above the transition altitude, use standard pressure 1013.25 hPa and flight levels. “High to low, look out below”: flying toward lower pressure without resetting the altimeter makes the true altitude lower than indicated. Temperature also affects true altitude. METAR reports observed conditions; TAF gives a forecast valid for a stated period. Winds in METAR/TAF are true, while tower and ATIS winds are normally magnetic.
Worked example
Runway 27 has heading 270°. Wind is 300° at 20 kt, so the angle between runway and wind is 30°. Crosswind = 20 × sin 30° = 10 kt. Headwind = 20 × cos 30° = 17 kt. The crosswind is within a typical light-aircraft limit, but check the aircraft flight manual. For pressure altitude, if QNH is 1000 hPa and elevation is 1,000 ft, pressure altitude ≈ 1,000 + (1013 − 1000) × 30 = 1,390 ft.
Traps
Do not confuse QNH and QFE. Do not use indicated altitude as true altitude in cold air or low pressure. Check whether wind is true or magnetic. Remember that TAF validity is a forecast period, not an observation time. Crosswind components must be calculated for the actual runway, not the runway you planned.