Meteorology
Atmosphere and stability
Know the standard atmosphere, lapse rates, and how stability governs cloud type and turbulence. Unstable air gives cumuliform cloud, showers, and gusty surface wind; stable air gives stratiform cloud and smooth air but poor visibility in haze.
Wind and local effects
Understand gradient versus surface wind, the Ekman spiral, and why surface wind backs and decreases with friction. Learn mountain and valley winds, anabatic and katabatic flow, and the venturi effect in passes. Helicopters are highly exposed to mechanical turbulence near buildings and to rotor downwash recirculation in confined areas.
Icing and hazards
Know airframe icing types (rime, clear, mixed), carburettor icing ranges, and that helicopter rotor blades and intakes are vulnerable before the airframe shows ice. Trap: questions that assume icing only occurs below freezing at the surface - it can occur in supercooled cloud well above 0 °C ambient at the aircraft.
Worked example
A forecast of 2,500 ft cloud base with a temperature/dewpoint spread of 1 °C suggests imminent lowering. Rule of thumb: a spread of 2 °C or less means fog or low cloud is likely within the hour; plan a diversion rather than pressing on.