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A book that contains astronomical or meteorological data arranged according to days, weeks, and months of a given year and may also include diverse information of a nonastronomical character. This article is restricted to astronomical and…

Any device which measures the height of an aircraft. The two chief types are the pressure altimeter, which measures the aircraft's distance above sea level, and the radar altimeter, which measures distance above the ground. Pressure Altimeter A…

An anchored or moored floating object, other than a lightship, intended as an aid to navigation. Buoys are the most numerous of all engineered aids to navigation, with some 20,000 in United States waters alone.A great variety of buoys are in use.…

In early 2018, NASA announced that it had demonstrated a new type of celestial navigation for the first time. Called XNAV, for x-ray pulsar-based navigation, it relies on beams of radiation from pulsars—the cinders of exploded, massive stars. As…

One of the most remarkable features of the sea (marine) turtles that inhabit the tropical and subtropical waters of the world is their homing ability. Throughout the year, sea turtles swim huge distances, often more than 1600 kilometers (1000…

A discipline that combines the means to know the location and heading of an aircraft with respect to some map or coordinate system, with guidance which means steering the aircraft along some desired path toward a destination. The construction of…

A service to promote the safe, orderly, and expeditious flow of air traffic. Safety is principally a matter of preventing collisions with other aircraft, obstructions, and the ground; assisting aircraft in avoiding hazardous weather; assuring that…

A device that reduces the risk of midair collision by providing advisories to the flight crew. It is known in the United States as a Traffic Alert and Collision Avoidance System (TCAS), and operates independently of the ground-based air-traffic…

An instrument that indicates the bearing, or angle of the direction in which an aircraft is pointing in the horizontal plane. A compass may indicate magnetic heading or bearing, bearing referenced to a radio signal source, or bearing with respect to…

A coordinated group of instruments that provides the flight crew with information about the aircraft and its subsystems. Together with the controls, aircraft instruments form the human–machine interfaces that enable the flight crew to operate the…

A ground mapping system that uses analog radar equipment to provide surveillance of aircraft and other surface vehicles on an airport surface. It is used by air-traffic controllers in airport control towers to monitor and control the movement of…

A device that computes and displays speed of an aircraft relative to the air mass in which the aircraft is flying. Three common types are the indicated airspeed meter, true airspeed indicator, and Machmeter.The commonest type is the indicated…

The satellite navigation systems GPS (the U.S.–managed Global Positioning System) and GLONASS (the Russian global navigation satellite system) have been operational in some form for decades. Other global and regional navigational satellite systems…

A device that provides the pilot with symbols representative of the attitude of an aircraft relative to an artificial horizon. In an automatic or artificial horizon a vertical gyro moves a horizon bar relative to a fixed aircraft index. Motion of…

The means for guiding and controlling aircraft from an initial approach altitude to a point where safe contact is made with the landing surface. Such systems differ from low-approach systems in three major respects: (1) They furnish not only…