Meteorology for navigation
Meteorology for navigation
This domain tests the weather knowledge that changes a nav log: altimetry, wind, temperature and the synoptic patterns around NZ.
Altimetry. QNH is the pressure at sea level; QFE is station pressure; QNE is the standard setting 1013.2 hPa. 1 hPa ≈ 30 ft. "High to low, look out below": flying from high pressure to low without resetting the altimeter leaves the aircraft lower than indicated. In cold air, true altitude is lower than indicated - the altimeter over-reads.
NZ patterns. The prevailing westerlies and the Southern Alps produce mountain waves and severe lee turbulence east of the divide, plus the Canterbury nor'wester and Föhn conditions. In the Southern Hemisphere, lows circulate clockwise and anticyclones anticlockwise; with your back to the wind, low pressure is on your right (Buys Ballot).
Forecasts. Decode METAR/TAF for wind, visibility, cloud and QNH; use GAF, SIGMET and AIRMET for enroute hazards. Winds aloft are forecast in degrees true and knots.
Worked example. Aerodrome elevation 1,000 ft, QNH 1000 hPa. With 1013 set in the subscale, the altimeter reads pressure altitude = 1,000 + 30 × (1013 − 1000) = 1,390 ft. The aircraft is 390 ft higher than the altimeter indicates relative to the aerodrome; on approach with QNH set, the altimeter reads 1,000 ft on the ground.
Traps. Mixing QFE and QNH; applying the 30 ft/hPa rule in the wrong direction; using magnetic winds aloft (they are true); and ignoring temperature error on high-elevation approaches.