air navigation definition of air navigation in the Free Online Encyclopedia.

air navigation, science and technology of determining the position of an aircraft with respect to the surface of the earth and accurately maintaining a desired course (see navigation navigation, science and technology of finding the position and directing the course of vessels and aircraft.

Early Navigational Techniques

In ancient times, mariners navigated by the guidance of the sun and stars and landmarks along the coast.
..... Click the link for more information. ).

Visual and Instrument Flight

The simplest and least sophisticated way to keep track of position, course, and speed is to use pilotage, a method in which landmarks are noted and compared with an aeronautical chart. Whether these landmarks are observed visually or on radar, this technique of air navigation is usually called flying under visual flight regulations (VFR). These establish the minimum weather conditions under which pilotage is permissible.

Pilotage is not satisfactory for long trips, especially over water or terrain lacking distinctive features. In these cases, or when weather conditions do not permit navigation by visual reference, planes must fly according to instrument flight regulations (IFR), which require that the aircraft be equipped with the necessary position-finding instruments and that the pilot be trained in operating those instruments. Also required under IFR is the filing of a flight plan with air traffic control air traffic control, the system by which airplanes are safely routed into and out of major airports. Air traffic control in the United States is centered in a number of regional control centers that route airplanes along established airways to airport traffic control
..... Click the link for more information. authorities at the departure point. The aircraft is then cleared for a given course and a given altitude. Air traffic controllers monitor the craft until it reaches its destination.

Aircraft Instruments

Light aircraft, flown by pilotage, typically have a simple set of navigational instruments, including an airspeed indicator (see pitot static system pitot static system (pētō`), device for measuring the rate at which a fluid flows.
..... Click the link for more information. ), an aneroid altimeter, and a magnetic compass. For supersonic and hypersonic aircraft the airspeed indicator is altered to show the airspeed as a Mach number Mach number (mäk) [for E. Mach ], ratio between the speed of an object and the speed of sound in the medium in which the object is
..... Click the link for more information. , which is the ratio of the speed of an aircraft to the speed of sound. Advanced aircraft also use electronic systems to give the pilot highly accurate positional information for use during landing. The Instrument Landing System enables an airplane to navigate through clouds or darkness to an airport's runway; the Microwave Landing System, installed in U.S. airports beginning in 1988, is capable of landing the plane automatically, although the pilot always has the option of overriding manually.

Other navigational aids include the radio altimeter altimeter (ăltĭm`ĭtər, ăl`tĭmē'tər), device for measuring altitude.
..... Click the link for more information. , a radar device that indicates the distance of the plane from the ground; the ground-speed indicator, which operates by measuring the Doppler shift in a radio wave reflected from the ground; and, in commercial airliners, the flight management computer, which can display altitude, speed, course, wind conditions, and route information, as well as monitor the airplane's progress through the airway. Other similar systems use inertial devices such as free-swinging pendulums and gyroscopes as references in determining position. These automated and semiautomated procedures free the pilot from many of the activities previously necessary for navigation and thus allow the pilot to concentrate on actually flying the aircraft. Another device which is useful in this way is the automatic pilot, which interprets data on direction, speed, attitude, and altitude to maintain an aircraft in straight, level flight on a given course at a given speed.

Airways and Radio Ranges

Basic to air traffic control are special air routes called airways. Airways are defined on charts and are provided with radio ranges radio range, geographically fixed radio transmitter that radiates coded signals in all directions to enable aircraft and ships to determine their bearings. An aircraft or ship can determine its line of position and drift if it knows its bearing relative to the radio
..... Click the link for more information. , devices that allow the pilot whose craft has a suitable receiver to determine the plane's bearing and distance from a fixed location. The most common beacon is a very high frequency omnidirectional radio beacon, which emits a signal that varies according to the direction in which it is transmitted. Using a special receiver, an air navigator can obtain an accurate bearing on the transmitter and, using distance-measuring equipment (DME), distance from it as well.

The system of radio ranges around the United States is often called the VORTAC system. For long distances other electronic navigation systems have been developed: Omega, accurate to about two miles (3 km); Loran-C, accurate to within .25 mi (.4 km) but available only in the United States; and the Global Positioning System (GPS), a network of 24 satellites that is accurate to within a few yards and is making radio ranging obsolete.

Bibliography

See J. Elliott and G. Guerny, Pilot's Handbook of Navigation (1977).