Glossary

Differential ailerons. Control surface rigged such that the DME arc. A flight track that is a constant distance from the aileron moving up moves a greater distance than the aileron station or waypoint. moving down. The up aileron produces extra parasite drag to compensate for the additional induced drag caused by DOD. Department of Defense. the down aileron. This balancing of the drag forces helps minimize adverse yaw. Doghouse. A turn-and-slip indicator dial mark in the shape of a doghouse. Differential Global Positioning System (DGPS). A system that improves the accuracy of Global Navigation Satellite Domestic Reduced Vertical Separation Minimum Systems (GNSS) by measuring changes in variables to (DRVSM). Additional flight levels between FL 290 and FL provide satellite positioning corrections. 410 to provide operational, traffic, and airspace efficiency. Differential pressure. A difference between two pressures. Double gimbal. A type of mount used for the gyro in an The measurement of airspeed is an example of the use of attitude instrument. The axes of the two gimbals are at right differential pressure. angles to the spin axis of the gyro, allowing free motion in two planes around the gyro. Dihedral. The positive acute angle between the lateral axis of an airplane and a line through the center of a wing DP. See departure procedure. or horizontal stabilizer. Dihedral contributes to the lateral stability of an airplane. Drag. The net aerodynamic force parallel to the relative wind, usually the sum of two components: induced drag Diluter-demand oxygen system. An oxygen system that and parasite drag. delivers oxygen mixed or diluted with air in order to maintain a constant oxygen partial pressure as the altitude changes. Drag curve. The curve created when plotting induced drag and parasite drag. Direct indication. The true and instantaneous reflection of aircraft pitch-and-bank attitude by the miniature aircraft, Drift angle. Angle between heading and track. relative to the horizon bar of the attitude indicator. DRVSM. See Domestic Reduced Vertical Separation Direct User Access Terminal System (DUATS). A system Minimum. that provides current FAA weather and flight plan filing services to certified civil pilots, via personal computer, DUATS. See direct user access terminal system. modem, or telephone access to the system. Pilots can request specific types of weather briefings and other pertinent data Duplex. Transmitting on one frequency and receiving on a for planned flights. separate frequency. Directional stability. Stability about the vertical axis of an Dutch roll. A combination of rolling and yawing oscillations aircraft, whereby an aircraft tends to return, on its own, to that normally occurs when the dihedral effects of an aircraft flight aligned with the relative wind when disturbed from that are more powerful than the directional stability. Usually equilibrium state. The vertical tail is the primary contributor dynamically stable but objectionable in an airplane because to directional stability, causing an airplane in flight to align of the oscillatory nature. with the relative wind. Dynamic hydroplaning. A condition that exists when Distance circle. See reference circle. landing on a surface with standing water deeper than the tread depth of the tires. When the brakes are applied, there is Distance measuring equipment (DME). A pulse-type a possibility that the brake will lock up and the tire will ride electronic navigation system that shows the pilot, by an on the surface of the water, much like a water ski. When the instrument-panel indication, the number of nautical miles tires are hydroplaning, directional control and braking action between the aircraft and a ground station or waypoint. are virtually impossible. An effective anti-skid system can minimize the effects of hydroplaning. DME. See distance measuring equipment. G-10