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DEAD STICK - A term used to describe unpowered flight (glide) when the engine quits running.

DECISION ALTITUDE (DA) - A specified altitude in an instrument approach procedure at which the pilot must decide whether to initiate an immediate missed approach if the pilot does not see the required visual reference, or to continue the approach. Decision altitude is expressed in feet above mean sea level.

DECISION HEIGHT (DA) - A specified height above the ground in an instrument approach procedure at which the pilot must decide whether to initiate an immediate missed approach if the pilot does not see the required visual reference, or to continue the approach. Decision height is expressed in feet above ground level.

DIHEDRAL - The acute angle, usually upward, between the wing of an airplane and a horizontal cross-section line.

DIRECTIONAL GYRO - A panel instrument providing a gyroscopic reading of an aircraft's compass heading.

DIRECTIONAL STABILITY - The tendency of an aircraft to keep flying the direction it's pointed.

DIRIGILE - A lighter-than-air craft capable of being propelled and steered for controlled flight.

DIRTY - Extension of gear, hook, flaps, etc. for slow speed flight or landing.

DITCH - To land safely somewhere other than a runway.

DIVERT - To change from a scheduled landing base to an alternate airfield.

DME - Distance Measuring Equipment, a radio navigation device that determines the aircrafts distance from a ground station, as well as its groundspeed and time to/from the station.

DOWNWASH - The air deflected perpendicular to the direction of movement of an airfoil.

DRAG - The resisting force exerted on an aircraft in its line of flight opposite in direction to its motion.

DRIFT - The angle between the heading of an aircraft and its Track, or flight path, over the ground as affected by winds.