Glossary

Groundspeed. Speed over the ground, either closing speed to Height above landing (HAL). The height above a designated the station or waypoint, or speed over the ground in whatever helicopter landing area used for helicopter instrument direction the aircraft is going at the moment, depending upon approach procedures. the navigation system used. Height above touchdown elevation (HAT). The DA/DH or GS. See glideslope. MDA above the highest runway elevation in the touchdown zone (first 3,000 feet of the runway). GWPS. See ground proximity warning system. HF. High frequency. Gyroscopic precession. An inherent quality of rotating bodies, which causes an applied force to be manifested 90° in the Hg. Abbreviation for mercury, from the Latin hydrargyrum. direction of rotation from the point where the force is applied. High performance aircraft. An aircraft with an engine of H more than 200 horsepower. HAA. See height above airport. Histotoxic hypoxia. The inability of cells to effectively use oxygen. Plenty of oxygen is being transported to the cells HAL. See height above landing. that need it, but they are unable to use it. HAT. See height above touchdown elevation. HIWAS. See Hazardous Inflight Weather Advisory Service. Hazardous attitudes. Five aeronautical decision-making Holding. A predetermined maneuver that keeps aircraft attitudes that may contribute to poor pilot judgment: anti- within a specified airspace while awaiting further clearance authority, impulsivity, invulnerability, machismo, and from ATC. resignation. Holding pattern. A racetrack pattern, involving two turns Hazardous Inflight Weather Advisory Service (HIWAS). and two legs, used to keep an aircraft within a prescribed An en route FSS service providing continuously updated airspace with respect to a geographic fix. A standard pattern automated of hazardous weather within 150 nautical miles of uses right turns; nonstandard patterns use left turns. selected VORs, available only in the conterminous 48 states. Homing. Flying the aircraft on any heading required to keep Head-up display (HUD). A special type of flight viewing the needle pointing to the 0° relative bearing position. screen that allows the pilot to watch the flight instruments and other data while looking through the windshield of the Horizontal situation indicator (HSI). A flight navigation aircraft for other traffic, the approach lights, or the runway. instrument that combines the heading indicator with a CDI, in order to provide the pilot with better situational awareness Heading. The direction in which the nose of the aircraft is of location with respect to the courseline. pointing during flight. Horsepower. The term, originated by inventor James Watt, Heading indicator. An instrument which senses airplane means the amount of work a horse could do in one second. movement and displays heading based on a 360° azimuth, One horsepower equals 550 foot-pounds per second, or with the final zero omitted. The heading indicator, also called 33,000 foot-pounds per minute. a directional gyro (DG), is fundamentally a mechanical instrument designed to facilitate the use of the magnetic Hot start. In gas turbine engines, a start which occurs with compass. The heading indicator is not affected by the forces normal engine rotation, but exhaust temperature exceeds that make the magnetic compass difficult to interpret. prescribed limits. This is usually caused by an excessively rich mixture in the combustor. The fuel to the engine must Headwork. Required to accomplish a conscious, rational be terminated immediately to prevent engine damage. thought process when making decisions. Good decision- making involves risk identification and assessment, HSI. See horizontal situation indicator. information processing, and problem solving. HUD. See head-up display. Height above airport (HAA). The height of the MDA above the published airport elevation. G-14