H

Heat barrier. See Thermal barrier.

Helicopter. An aircraft capable of both vertical and horizontal flight, which derives both lift and thrust from rotating wings power-driven about a vertical axis.

High-wing monoplane. An airplane whose wing is mounted at, near, or above the top of the fuselage. A parasol monoplane has its wing mounted above the fuselage on struts.

Hypoxia. Oxygen deficiency in the blood in high-altitude flight, impairing faculties

I

Icing. Atmospheric moisture freezing on the surfaces of an aircraft.

Instrument flight rules (IFR). Traffic and procedure rules governing flight under instrument conditions.

Instrument flying. Navigating and controlling an aircraft solely by the use of instruments.

Instrument Landing System (ILS). Radio system for guiding aircraft in landing during poor visibility. Directional radio transmitters indicate direction of runway and angle of glide path, and radio marker beacons establish position along approach path.

J

Jet. See Turbofan; Turbojet

Jet stream. 1. Narrow band of highspeed wind in upper troposphere or in stratosphere moving west to east. 2. Stream of combustion products expelled from a reaction engine.