Aeronautical Meteorology
What the controller must know
Meteorology affects separation, runway selection and safety. Know the METAR/TAF format, the meaning of QNH, QFE, QNE, and how altimeter settings are used. Understand wind (direction, speed, gusts, shear), visibility, RVR, cloud (base and amount), and weather phenomena (rain, snow, fog, thunderstorms). Know the ICAO weather categories for low visibility (CAT I, II, III) and how they relate to approach minima.
Hazardous weather
Know wind shear and microburst hazards, icing conditions, turbulence categories, and thunderstorm hazards including lightning and hail. Understand SIGMET and AIRMET and when they are issued. Know the ISA standard atmosphere and how temperature affects altimeter and performance.
Traps and a rule of thumb
Traps: confusing QNH (altitude above mean sea level) with QFE (height above aerodrome); misreading RVR versus visibility; forgetting that a TAF is a forecast and METAR is an observation; and misapplying CAT I/II/III minima. Rule of thumb: QNH gives altitude, QFE gives height above the aerodrome, QNE is standard pressure at 1013.25 hPa used above the transition level. Worked example: if the aerodrome QNH is 1013 hPa and the aircraft is on the ground, the altimeter reads aerodrome elevation; if QFE is set, it reads zero.