Dead reckoning. Calculation of position using earlier known position, elasped time, speed, heading, and wind.

Deicer. Device for removing ice from wings, propeller, or control surfaces.

Dihedral. Upward (positive) or downward (negative) inclination of a wing or stabilizer from the horizontal.

Drag. Resistance to the passage of an airplane through the air.

E

Ejection seat. A seat designed to be catapulted with its occupant high-speed aircraft in an emergency

Elevator. A control surface hinged to a horizontal stabilizer for rotating an aircraft about its lateral axis

Empennage, or tail assembly. Horizontal and vertical stabilizers and control surfaces at rear of an aircraft

F

Feather. 1. To turn a propeller balade edgewise into the airflow to minimize resistance. 2. To change a blade angle or a rotor blade or rotating wing

Flap. A movable control surface at rear of wing for increasing lift or drag in takeoff or landing.

Flight plan. A detailed statement about a proposed flight submitted to Air Traffic Control prior to takeoff, including point of departure and destination, flight route, altitude, and airspeed.

Free fall. The drop of a parshutist before opening his parachute.

Fuselage. The main body of an airplane.

G

G-force. A force exerted by gravity or by reaction to acceleration or deceleration when direction is changed. Measured in g's, or multiples of force of gravity.

Glide path. The line of flight of aircraft in controlled descent.

Ground controlled approach (GCI) An instrument landing system, used during poor visibility in which a ground operator observes a plane's position and direction on a radarscope and directs the pilot by radio.

Ground loop. A violent turn while moving on the ground.

Gull wing. A wing which slants upward from its roots and then flattens out or angles upward. An inverted gull wing slants downward and then straightens out or slants upward.