Navigation, Air

the science of the methods and equipment for guiding aircraft (airplanes, helicopters, missiles, and so on); the aggregate of operations used by ground control or on-board facilities to determine navigational elements, and also their use to guide the aircraft. The principles of air navigation originated in sea navigation, which was developed in ancient times. In particular, the method of the magnetic compass and nautical astronomy were borrowed from it.

Air navigation ensures that an aircraft is guided along a trajectory determined by the flight route and profile, according to a prescribed plan that regulates the flight conditions from takeoff to landing at a prescribed time. In addition, air navigation solves particular navigation problems, such as the maintenance of prescribed distances and time intervals between aircraft on routes with dense air traffic or upon leaving a route for a landing approach, the prevention of collisions of airplanes with terrain obstacles (such as mountains), and the convergence of two aircraft in flight (for example, a rendezvous with a tanker for refueling). When a flight is carried out according to a predetermined route and plan, the task of air navigation, in contrast to pilotage, reduces primarily to the acquisition of continuous or periodic information on the current navigational elements of the translational motion of the center of mass of the aircraft with respect to a coordinate system correlated to the surface of the earth.

Various types of equipment are used to determine the navigational elements (including course, drift angle, course angle, airspeed and ground speed, altitude, and the coordinates of the aircraft’s location). The equipment is divided into four main groups, according to the primary source of navigational information as follows.

(1) Geotechnical devices, which make possible determination of the relative altitude of flight, the magnetic course, and the location of the aircraft by measuring various parameters of the earth’s geophysical fields (such as the magnetic and gravitational fields). Such equipment includes altimeters, devices for measuring airspeed and ground speed, magnetic and gyromagnetic compasses, directional gyroscopes, optical sights, and inertial navigation systems.

(2) Radio aids, which make possible determination of the true altitude, ground speed, and location of an aircraft by measuring various parameters of the electromagnetic field on the basis of radio signals from special transmitters. Such aids include radio altimeters, radio beacons, radio compasses, and radio navigation systems.

(3) Astronomical equipment, which makes possible determination of the course and location of an aircraft. This includes astrocompasses, sextants, and stellar trackers.

(4) Illumination devices, which are intended to facilitate the landing of aircraft under complex weather conditions and at night, and also to facilitate orientation (beacons).

Since advantages and shortcomings are inherent in each group of technical navigational aids, aids that use various principles are combined as sensors to form unified integrated systems to ensure the accurate flight of an aircraft along a prescribed route under any weather conditions. In such systems the main navigation problems are solved by means of analog or digital computers, and a flight plan is drawn up (including such factors as the coordinates of the points on the route, the altitudes and speeds of flyover of points, and the coordinates of radio navigation systems). Integrated navigation systems that are linked to an autopilot can accomplish automatic flight over the entire route, and also a landing approach, even when the surface of the earth cannot be seen. The integrated navigation system usually determines the position of the aircraft on the basis of three coordinates: two are the projections of the aircraft’s center of mass onto a horizontal plane (longitude and latitude), and one is the altitude. To orient an aircraft it is sufficient to know the two coordinates in the horizontal plane. The flight route is monitored on the basis of the route line, which is determined by a projection of the ground speed vector. This vector is found by adding the measured vectors of airspeed (the speed of the aircraft with respect to the air) and the speed of movement of the air with respect to the surface of the earth. The altitude is measured with an altimeter.

Various methods are used to determine the instantaneous coordinates of the aircraft’s position in flight. The three main methods are as follows: (1) dead reckoning, which is based on determination of the lines (surfaces) of the aircraft’s position by discrete or continuous summation of its measured velocity or acceleration over time; (2) the positional method (position lines), which is used for direct determination of the position lines (surfaces) of an aircraft without taking into consideration the distance it has traveled, by finding the coordinates of the aircraft’s position with respect to known ground reference points or heavenly bodies; (3) the comparative scanning method (orientation), which is used to determine an aircraft’s location either by comparing the actually observed picture of the terrain according to identified ground reference points (including visual, radar, and magnetic references) with a geographic map or standard model of the terrain or by comparing a section of the sky with a star chart. The specific characteristics of the guidance of various types of aircraft, and also the class and function of the aircraft, the regions where the craft are used, and the nature of the route, determine the composition of integrated air navigation systems. The equipment and methods to be used in air navigation are selected in accordance with a plan drawn up in advance by the navigator.

The necessity of ensuring the greatest possible safety of air traffic in spite of its increasing density, the growth in the number and length of air routes, and the further increase in the flying speeds of aircraft has led to the development and introduction of automatic integrated systems for air navigation and air traffic control.