Meteorology and winds affecting navigation
This domain tests how New Zealand weather and winds affect navigation planning and in-flight decisions. Expect questions on METAR/TAF, GAF, SIGMET, winds aloft, QNH, drift, mountain wave, sea breezes and density altitude.
Core rules
- Read the validity, issue time and trend of each product. METAR/TAF, GAF and SIGMET are not interchangeable; a SIGMET affects the planned route immediately.
- Forecast winds are direction true and speed in knots. Convert to magnetic before applying to a magnetic heading, and use the wind at the planned altitude, not the surface wind.
- QNH gives altitude above mean sea level; use the forecast/actual QNH for terrain clearance. Density altitude affects climb and landing performance, especially on hot high aerodromes.
- In New Zealand, prevailing westerlies and mountain ranges produce lee turbulence and mountain wave. Sea breezes, fronts and squalls can change wind quickly; plan an alternate and extra fuel.
Worked example
Track 360°T, TAS 120 kt, wind 270°/30 kt true at 5000 ft, variation 20°E. Wind is from the left, so drift is right. Crosswind = 30 kt; drift = arcsin(30/120) = 14.5°. Heading = 360 − 14.5 = 345.5°T; magnetic = 345.5 − 20 = 325.5°M, round to 326°M. GS = sqrt(120² − 30²) = 116 kt. For 60 NM, time = 60/116 × 60 = 31 min. If the actual wind is stronger, drift and time change, so revise.
Traps
Treating a true forecast wind as magnetic; using surface wind for cruise; ignoring mountain wave; using an old QNH; misreading TAF validity; and failing to act on SIGMET or changing conditions.