A number representing the ratio of the speed of an object to the speed of sound in the surrounding air or medium in which it is moving.

The most common liquid-type compass, capable of calibration to compensate for magnetic influences within the aircraft.

COMPASS COURSE ± deviation

The magnetic North pole, located near 71° North latitude and 96° West longitude, that attracts a magnetic compass which is not influenced by local magnetic attraction, as opposed to GEOGRAPHIC NORTH.

An accessory that produces and distributes a high-voltage electric current for ignition of a fuel charge in an internal combustion engine.

The effect on a spinning cylinder or sphere moving through a fluid, in which force acts perpendicular to the direction of motion and to the direction of spin. This is used to advantage in baseball, in which the trajectory of a pitched ball is a distinct curve. Applied to aeronautics in experimental wingforms, the Magnus Theory states that if air is directed against a smooth, revolving cylinder, whose circumferential speed is greater than that of the air current, a force is directed against one side of the cylinder — air compressed on one side and vacuum formed on the other — creating lift. Named after physicist Heinrich Gustav Magnus (1802-70).

SEE RADIO NAVIGATION

SEE MSL

SEE SPECIAL USE AIRSPACE

Type of fuselage design with little or no internal bracing other than bulkheads, where the outer skin bears the main stresses; usually round or oval in cross-section. Additional classifications are (1) Semi-Monocoque, where the skin is reinforced by longerons or bulkheads, but with no diagonal web members, and (2) Reinforced Shell, in which the skin is supported by a complete framework or structural members. French: monocoque,single shell.

Mean Sea Level. The average height of the surface of the sea for all stages of tide; used as a reference for elevations, and differentiated from AGL.