IFR (Instrument Flight Rules)— Rules that govern the procedure for conducting flight in weather conditions below VFR weather minimums. The term IFR also is used to define weather conditions and the type of flight plan under which an aircraft is operating.

Piston powered helicopters use a heat exchanger shroud around the exhaust manifold to provide cabin heat. Outside air is piped to the shroud and the hot exhaust manifold heats the air, which is then blown into the cockpit. This warm air is heated by the exhaust manifold but is not exhaust gas. Turbine helicopters use a bleed air system for heat. Bleed air is hot, compressed, discharge air from the engine compressor. Hot air is ducted from the compressor to the helicopter cabin through a pilot-controlled, bleed air valve.

Most anti-icing equipment installed on small helicopters is limited to engine intake anti-ice and pitot heat systems.

The anti-icing system found on most turbine-powered helicopters uses engine bleed air. The bleed air flows through the inlet guide vanes to prevent ice formation on the hollow vanes. A pilot-controlled, electrically operated valve on the compressor controls the air flow. The pitot heat system uses an electrical element to heat the pitot tube, thus melting or preventing ice formation.

Airframe and rotor anti-icing may be found on some larger helicopters, but it is not common due to the complexity, expense, and weight of such systems. The leading edges of rotors may be heated with bleed air or electrical elements to prevent ice formation. Balance and control problems might arise if ice is allowed to form unevenly on the blades. Research is being done on lightweight ice-phobic (anti-icing) materials or coatings.

These materials placed in strategic areas could significantly reduce ice formation and improve performance.