Aviation Glossary

M&D (Malfunction and Defect) report. A small postcard-like form (FAA Form 8330) used by repair stations, maintenance shops, and technicians to report an unacceptable condition to the FAA. Information on these forms provides the basis for the General Airworthiness Alerts and subsequent Airworthiness Directives. Mach number. The ratio of the speed of an object through … Read more

Labyrinth seal. A type of air and/or seal used around the main –shaft bearings in a gas turbine engine. The seal consists of a series of rotating blades that almost contact the seal land. A small amount of air flows between the seal and the land to prevent oil flowing past the seal. L/D ratio. … Read more

Jet fuel. Fuel designed and produced to be used in aircraft gas turbine engines. Jet propulsion. A method of propulsion by accelerating a relatively small mass of air through a large change in velocity. Jeweler’s file. A small, fine-cut, metalworking file used by jewelry manufacturers. Joule. A measure of energy. In terms of electrical energy, … Read more

Ice bridging. A spark plug failure that occurs when starting a reciprocating engine in extremely cold weather. When a cylinder fires, the fuel-air mixture is converted into carbon dioxide and water vapor. The water vapor condenses on the spark plug electrodes and forms ice that bridges the electrode gap and prevents the plug firing until … Read more

Halon 1211. A halogenated hydrocarbon fire-extinguishing agent used in many HRD fire-extinguishing systems for powerplant protection. The technical name for Halon 1211 is bromochlorodifluoromethane. Half-wave rectifier. An electrical rectifier circuit that converts AC into pulsating DC. Only one alternation of each cycle is present in the output. Halogenated hydrocarbon. A hydrocarbon compound in which one … Read more

Galling. Fretting or pulling out chunks of a surface by sliding contact with another surface or body. Gas generator. The basic gas turbine engine. It consists of the compressor, diffuser, combustor, and turbine. The gas generator is also called the core engine. Gas turbine engine. An internal combustion engine that burns its fuel in a … Read more

FAA Form 337. The Major Repair and Alteration form that must be completed when an FAA-certificated aircraft or engine has been given a major repair or major alteration. Face (propeller nomenclature). The flat surface of a propeller that strikes the air as the propeller rotates. The face of a propeller corresponds to the bottom of … Read more

EADI. Electronic Attitude Director Indicator. ECAM. Electronic Centralized Aircraft Monitor. Eccentric brushing. A special bushing used between the rear spar of certain cantilever airplane wings and the wing attachment fitting on the fuselage. The portion of the bushing that fits through the hole in the spar is slightly offset from that which passes through the … Read more

Dacron. The registered trade name for a cloth woven from polyester fibers. Damped oscillation. Oscillation whose amplitude decreases with time. Data bus. A wire or group of wires that are used to move data within a computer system. Data. The input for computer processing in the form of numerical information that represents characters or analog … Read more

Cage (verb). To lock the gimbals of a gyroscopic instrument so it will not be damaged by abrupt flight maneuvers or rough handling. Calendar month. A measurement of time used by the FAA for inspection and certification purposes. One calendar month from a given day extends from that day until midnight of the last day … Read more