Meteorology
Domain 3 tests altimetry and hazardous weather: how pressure settings change what the altimeter shows, and how METAR, TAF, SIGMET and wind shear reports affect your control decisions.
Altimetry rules
Below the transition altitude, aircraft use QNH; on the aerodrome, QFE may be used. At and above the transition level, aircraft fly flight levels with 1013.2 hPa set. One hectopascal is about 27 ft. High temperature makes true altitude higher than indicated altitude, which matters on a hot approach. The transition altitude and transition level vary by aerodrome and are published.
Hazardous weather
Thunderstorms bring turbulence, hail, icing, microbursts and wind shear. Dust and haze reduce visibility in the region; Shamal winds can produce widespread blowing dust. Mountain waves affect approaches near high terrain. SIGMET warns of phenomena such as severe turbulence, volcanic ash and tropical cyclones; AIRMET covers less severe conditions.
Worked example: aerodrome elevation 3,900 ft, QNH 1003 hPa. QFE = 1003 − (3,900 ÷ 27) ≈ 1003 − 144 = 859 hPa. On the ground with QNH set, the altimeter reads 3,900 ft; with QFE set, it reads 0 ft. If the crew leaves 1013 hPa set, the altimeter reads about 4,170 ft on the ground, 270 ft high.
Traps: using QFE at a flight level; leaving QNE set below the transition level; ignoring temperature correction on a hot approach; treating a TAF as a current observation.