CAA NZ ATPL Theory - Flight Navigation General key terms

Calculating present position by advancing a known starting point using elapsed time, heading and speed, without fixing on external features or radio aids. Wind and compass errors must be applied separately.

Vector diagram combining true airspeed along heading, wind velocity, and the resultant ground speed along track. Solving it yields heading and ground speed for a required track.

Direction and speed of the air mass expressed as a velocity, conventionally given as the direction the wind blows from. It is added to the air vector to give the ground vector.

Angle between heading and track needed to counter drift caused by wind. It is applied into wind, and its sign depends on whether the wind is from left or right of track.

Angle between the aircraft's heading and the track actually made good over the ground. It results from wind and is normally expressed as left or right of heading.

The path of the aircraft over the ground, measured from a reference direction. True track uses true north; magnetic track is true track corrected for local magnetic variation.

The direction the aircraft nose points, referenced to true or magnetic north. Magnetic heading equals magnetic track plus or minus wind correction, then corrected for deviation.

Angular difference between true north and magnetic north at a given place, changing slowly with position and time. It is shown on charts as isogonals and applied when converting true to magnetic directions.

Error of a particular magnetic compass caused by the aircraft's own magnetic fields and electrical currents. It varies with heading and is recorded on a compass swing card.

A line on a chart joining places of equal magnetic variation. Where the line is marked 0 degrees the variation is zero and true and magnetic directions coincide.

The specific isogonal along which magnetic variation is zero, so true and magnetic bearings are identical. It currently runs through parts of North America and the Atlantic.

A procedure in which the aircraft is aligned on successive headings and residual deviation is measured and recorded on a deviation card. It is repeated periodically and after major electrical or structural changes.

A magnetic bearing from a VOR station, selected or displayed by the receiver. Flying a given radial inbound or outbound gives a defined magnetic track to or from the station.

A very high frequency navigation beacon that transmits phase information allowing an aircraft to determine its magnetic bearing from the station. Line-of-sight reception limits useful range at low altitude.

A transponder-based system measuring slant range from the aircraft to a ground station by timing interrogations and replies. Displayed distance is greater than ground distance, increasingly so at high altitude and close range.

The straight-line distance from aircraft to ground station, including height difference. DME indicates slant range, so it overreads compared with map distance, especially when close in.

A low or medium frequency beacon transmitting continuously so an aircraft's ADF can indicate the bearing of the station. Susceptible to static, night effect and coastal refraction.

Airborne receiver and loop antenna that continuously displays the relative bearing of a selected NDB. Combined with heading it gives magnetic bearing to the station.

Angle measured clockwise from the aircraft's nose to the bearing of a station. Adding relative bearing to heading gives the magnetic bearing to the station.

Direction of a station or object measured from magnetic north at the aircraft. It is obtained by adding relative bearing to magnetic heading.

Precision approach aid providing lateral guidance from a localiser and vertical guidance from a glide path, plus range markers. It is tuned to a single frequency and monitored for integrity.

The lateral guidance component of an ILS, transmitting on a VHF frequency to define the extended runway centreline. Its sensitivity increases as the aircraft approaches the threshold.

The vertical guidance component of an ILS, typically set at about three degrees to the runway. It is normally transmitted by a UHF aerial beside the touchdown zone.

Satellite constellations providing position, velocity and time worldwide. Aviation use requires augmentation or monitoring to assure integrity, accuracy and availability.

Receiver autonomous integrity monitoring, a function that checks satellite signals for consistency so the receiver can warn of a faulty satellite. It requires sufficient satellites in view.

Area navigation allowing flight on any desired path using inputs from various navigation aids rather than tracking directly to or from ground beacons. It requires defined performance for the airspace.

A navigation specification stating the accuracy, integrity and containment an aircraft must achieve for a route or procedure. It includes on-board performance monitoring and alerting.

A defined geographical position used to build an RNAV route or procedure. It may be a fly-by point, where turn anticipation applies, or a fly-over point.

Solar time at a particular longitude, based on the mean sun. It differs from UTC by four minutes for each degree of longitude, east ahead and west behind.

The standard time reference used in aviation and navigation, equivalent to mean solar time at the prime meridian. It is unaffected by seasonal clock changes.

Local clock time within a standard time zone, usually offset from UTC by whole hours. Pilots convert between zone time and UTC for flight planning and reporting.

The shortest path between two points on the Earth's surface, lying on a plane through the Earth's centre. Its direction changes continuously except along the equator or a meridian.

A line crossing every meridian at the same angle, appearing straight on a Mercator chart. It is a constant track but not the shortest distance on long routes.

A chart projection on which meridians are parallel and the scale expands with latitude so rhumb lines plot straight. Great circles appear curved except along the equator.

A chart projection using a cone intersecting the Earth, giving straight-line great circles approximately and near-constant scale along a standard parallel. Common for topographical and terminal charts.

Height above mean sea level. It differs from indicated altitude when temperature or pressure differs from standard, causing the altimeter to overread in cold air.

Altitude indicated when the altimeter subscale is set to standard pressure 1013.25 hPa. It is used for flight levels and performance calculations.

Adjustment applied to published minimum altitudes when temperature is below standard, because the altimeter overreads and true height is lower than indicated. Corrections grow with height above the station.

Speed over the ground obtained from rate of change of DME distance, or from wind triangle solution. DME-derived values are affected by slant range and station passage.