Meteorology
Meteorology tests the atmosphere, pressure and altimetry, wind, clouds, precipitation, fronts, icing, thunderstorms, fog and METAR/TAF interpretation. Norwegian weather adds coastal, orographic and winter icing challenges.
Core rules
- ISA: sea-level temperature 15 C, pressure 1013.25 hPa, lapse rate 1.98 C per 1,000 ft up to 11 km.
- QNH is pressure reduced to sea level; QFE is pressure at aerodrome level; standard setting is 1013.25 hPa.
- Wind is named by the direction from which it blows; backing is counterclockwise, veering is clockwise.
- Icing risk rises in supercooled cloud, freezing rain and high humidity; know airframe ice categories.
- Thunderstorms require instability, moisture and lift; avoid hail, microburst and lightning.
- METAR is observed weather; TAF is forecast; check validity, wind shear, visibility and cloud.
Worked example
Surface temperature is 15 C. At 5,000 ft in ISA, temperature = 15 minus (5 times 1.98) = 15 minus 9.9 = 5.1 C. If the actual temperature is 0 C, the air is colder than ISA and the altimeter over-reads in cold air; terrain clearance is less than indicated.
Traps
- Using QFE for en-route altimetry.
- Reading a TAF as current weather.
- Assuming visible moisture is required for all icing.
- Forgetting cold-temperature altimeter correction on approach.