CPL Navigation (Sri Lanka CAA Pilot Licence Examinations) key terms

The intended path of an aircraft over the ground, measured in degrees from true north. It describes where the aircraft should go, not where the nose points.

The direction the aircraft nose points, measured in degrees from true north. It equals true track adjusted for wind drift, so the aircraft follows the intended ground path.

The direction the aircraft nose points relative to magnetic north, obtained by applying magnetic variation to true heading. This is the value the compass should indicate after allowing for deviation.

The angular difference between true north and magnetic north at a given place, caused by the Earth's magnetic field. It changes with position and is shown on charts as isogonic lines.

The error of a particular magnetic compass caused by local magnetic fields in the aircraft, such as electrical wiring or metal structure. It is unique to each aircraft and read from a compass correction card.

The angular difference between heading and track, applied to counter the effect of wind. It is calculated from wind speed and direction relative to the aircraft's speed and intended track.

The angle between the aircraft's heading and the track actually made good over the ground, resulting from wind. It is what the pilot sees when comparing the nose direction with the ground path.

The actual path of the aircraft over the ground, determined from navigation fixes or by comparing heading and drift. It may differ from the planned track if wind or heading errors exist.

The direction in which the aircraft's longitudinal axis points, expressed in degrees from a chosen reference such as true or magnetic north. It is controlled by the pilot and differs from track when wind is present.

The direction of one point from another, measured in degrees from a reference north. In navigation it is used to describe the position of a station or waypoint relative to the aircraft.

The angle between the aircraft's heading and the direction to a station, measured clockwise from the nose. Adding relative bearing to heading gives the magnetic bearing to the station.

A chart projection on which meridians are parallel straight lines and the scale increases with latitude. Rhumb lines plot as straight lines, making it useful for marine and some air navigation.

A chart projection using a cone touching the Earth along standard parallels, on which great circles plot nearly as straight lines. It is common for aeronautical charts of mid-latitude areas.

The shortest path between two points on the surface of a sphere, formed by a plane passing through the Earth's centre. Its direction changes continuously along the route.

A path that crosses every meridian at the same angle, appearing as a straight line on a Mercator chart. It is not the shortest route but is easy to follow with a constant heading.

A unit of distance equal to one minute of latitude, approximately 1,852 metres. It is the standard unit for air and sea navigation because it relates directly to angular measurement on the Earth.

A unit of speed equal to one nautical mile per hour. It is used for airspeed, ground speed and wind speed in navigation calculations.

The speed of the aircraft over the ground, found by combining true airspeed with the wind component along the track. It determines how long a leg will take.

The speed of the aircraft through the air mass, corrected for altitude and temperature from indicated airspeed. It is used with wind to calculate ground speed and drift.

A method of estimating position by applying known heading, speed and elapsed time to a known starting point, with wind taken into account. It requires no external fixes but accumulates error over time.

A confirmed position determined from external references such as radio aids, visual landmarks or satellite navigation. It is used to update or correct a dead reckoning position.

A line on which the aircraft is known to lie, derived from a bearing, distance or other observation. Two or more position lines intersecting give a fix.

A ground-based radio navigation aid that transmits signals allowing an aircraft to determine the magnetic bearing of the aircraft from the station. It provides radial information for position fixing and tracking.

A magnetic bearing measured from a VOR station outwards, expressed in degrees. An aircraft flying along a given radial is on a specific magnetic track to or from the station.

A non-directional beacon that transmits a radio signal used by an aircraft's automatic direction finder to show the relative bearing to the station. It provides a simple but less precise navigation aid.

Distance measuring equipment that measures the slant range from the aircraft to a ground station by timing radio pulses. It gives distance in nautical miles, slightly greater than the horizontal distance at high altitude.

Instrument landing system providing lateral and vertical guidance to a runway, using a localiser and glide path. It allows precision approaches in low visibility.

The lateral guidance component of an ILS, transmitting a beam aligned with the runway centreline. It indicates whether the aircraft is left or right of the correct approach path.

The vertical guidance component of an ILS, normally set at about three degrees above the horizontal. It indicates whether the aircraft is above or below the correct descent profile.

A satellite-based navigation system that provides position, velocity and time worldwide. Receivers compute position from signals of several satellites, giving high accuracy fixes.

Receiver autonomous integrity monitoring, a function of GNSS receivers that checks whether the satellite signals are consistent and warns of faults. It is important for relying on GNSS for navigation.

A defined geographical point, identified by coordinates or a named navigation aid, used as a reference for planning or flying a route. Routes are built as sequences of waypoints.

The angular distance of a point north or south of the equator, measured from 0 to 90 degrees. One minute of latitude equals one nautical mile.

The angular distance of a point east or west of the prime meridian, measured from 0 to 180 degrees. Lines of longitude converge at the poles and define time zones.

Lines on a chart joining places of equal magnetic variation. They help pilots convert between true and magnetic directions for a given area.

The pressure reference set on an altimeter so that it indicates the correct altitude. It may be local pressure or standard pressure, depending on the phase of flight and the region.

The altitude at or below which the altimeter is set to local pressure and above which standard pressure is used. It separates altitude references from flight level references.

An altitude expressed in hundreds of feet with the altimeter set to standard pressure. It provides a common reference for aircraft above the transition altitude.