Meteorology
Meteorology tests whether you can turn weather data into flight decisions: altimeter settings, stability, icing risk, wind, and fluent METAR/TAF decoding. Expect calculation-style altimetry and practical judgement questions rather than pure recall.
Standard atmosphere and altimetry
- ISA at MSL: 15 °C, 1013.25 hPa, 1.225 kg/m³; lapse rate 1.98 °C per 1000 ft to 36,090 ft, then isothermal at −56.5 °C.
- Pressure falls roughly 1 hPa per 30 ft near MSL.
- QNH on the subscale makes the altimeter read airfield elevation; QFE reads height above a reference point; QNE is 1013.25 hPa, used above transition altitude.
- Flying from high to low pressure or high to low temperature makes true altitude lower than indicated: "high to low, look out below".
Stability, cloud and fog
- Compare the environmental lapse rate (ELR) with DALR 3.0 °C/1000 ft and SALR about 1.5 °C/1000 ft. ELR > DALR is absolutely unstable; ELR < SALR is absolutely stable; in between is conditionally unstable.
- Convective cloud base ≈ (temperature − dewpoint) × 400 ft per °C.
- Radiation fog needs clear skies, light wind and a moist surface cooling to dewpoint; advection fog needs warm moist air over a colder surface.
Icing and wind
- Airframe icing occurs in visible moisture between 0 and −20 °C, worst near −2 to −10 °C; carburettor icing can occur from −10 to +25 °C.
- METAR winds are true; ATIS and runway winds are magnetic.
Worked example
Field elevation 1000 ft, QNH 1003 hPa, altimeter set to 1013 hPa. The subscale is 10 hPa too high, so the altimeter over-reads by 10 × 30 = 300 ft and shows 1300 ft. With true elevation 1000 ft, the aircraft is 300 ft lower than indicated.
Traps
Using QFE instead of QNH when the field is above MSL; ignoring cold-air temperature error; treating a TAF as observed weather; reading METAR wind as magnetic; assuming any cloud means icing.