Meteorology
Pressure and altimetry
QNH is set to read elevation; QFE reads height above the aerodrome; standard 1013.25 hPa is used above the transition altitude. Roughly 1 hPa ≈ 30 ft near the surface (about 27 ft at low level). Flying from high to low pressure without resetting makes the altimeter over-read - the aircraft is lower than indicated.
Clouds and icing
Cumuliform cloud, showers and thunderstorms indicate instability; stratiform cloud and steady rain indicate stability. Airframe icing occurs between 0°C and about −20°C in visible moisture, worst around −2°C to −10°C. Wind shear and microbursts accompany cumulonimbus.
Reports and forecasts
METAR wind is true, a 10-minute mean with gusts, followed by visibility, weather, cloud, temperature/dewpoint and QNH. In a TAF, BECMG is a gradual change, TEMPO a temporary fluctuation, and FM an abrupt change.
Worked example
Aerodrome elevation 1,000 ft, QNH 1013 hPa. QFE ≈ 1013 − (1,000 ÷ 30) = 1013 − 33 = 980 hPa. On final with QNH set, the altimeter reads about 1,000 ft at touchdown.
Traps
Treating METAR wind as magnetic; treating TEMPO as covering the whole forecast period; mixing QFE and QNH in the circuit; forgetting the high-to-low, look-out-below rule.