ATPL General Navigation (061) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Oblate spheroid

The Earth model with equatorial radius 6,378.1 km and polar radius 6,357.0 km; flattening is 1/298.3, so the polar diameter is shorter than the equatorial diameter.

Great circle

A circle on the Earth's surface whose plane passes through the Earth's centre; it gives the shortest distance between two points and crosses each meridian at a different angle.

Rhumb line

A line of constant track that crosses every meridian at the same angle; it is longer than the great circle except along the equator or a meridian, and plots straight on a Mercator chart.

Departure formula

Departure in nautical miles equals change of longitude in minutes multiplied by the cosine of the mean latitude; it converts east-west angular distance into linear distance.

Magnetic variation

The angle between true north and magnetic north at a place, easterly when magnetic north lies east of true north; it varies with position and slowly with time.

Deviation

The angle between magnetic north and compass north caused by the aircraft's own magnetic fields; it depends on heading and is taken from the deviation card.

Compass conversion order

Compass, Deviation, Magnetic, Variation, True: add easterly deviation and variation when going from compass to true, subtract when converting true to compass.

Magnetic dip

The angle between the Earth's magnetic field and the horizontal; it is zero at the magnetic equator and 90 degrees at the magnetic poles, causing compass turning and acceleration errors.

Mercator projection

A conformal cylindrical projection on which rhumb lines plot as straight lines and great circles as curves concave toward the equator; scale increases with latitude by secant of latitude.

Lambert conformal conic

A conformal conic projection using one or two standard parallels; great circles are nearly straight and it is widely used for aeronautical charts of mid-latitude areas.

Chart scale

The representative fraction, such as 1:500,000, gives the ratio of chart distance to Earth distance; 1 cm on a 1:500,000 chart represents 5 km or 2.70 NM.

Contour line

A line joining points of equal elevation above a datum; the contour interval is the vertical distance between successive contours and shows the steepness of terrain.

Triangle of velocities

The vector sum of the air vector (heading and TAS) and the wind vector gives the ground vector (track and ground speed); it solves for drift and GS.

Drift angle

The angle between heading and track, positive to starboard; it equals the angle whose sine is wind speed times sine of wind angle divided by TAS.

Wind component

The headwind or tailwind component equals wind speed multiplied by the cosine of the angle between the wind and the track; the crosswind component uses the sine.

1 in 60 rule

A one-degree tracking error produces one nautical mile of off-track distance after 60 nautical miles; used for drift, track error and closing angle corrections.

Position line fix

A fix needs at least two position lines, ideally crossing at 60 to 90 degrees; three lines give a cocked hat that indicates the accuracy of the fix.

VOR radial

A magnetic bearing from a VOR station; two intersecting radials give a fix, and the radial is a straight position line from the station.

ADF relative bearing

The angle measured clockwise from the aircraft's magnetic heading to the NDB; true bearing equals magnetic heading plus relative bearing, then apply variation.

DME slant range

The line-of-sight distance from the aircraft to the DME station; it is greater than the ground distance, and the error grows with altitude and proximity to the station.

Point of no return

The furthest point from which the aircraft can return to departure with the fuel available, excluding reserves; distance equals fuel available times GS out divided by GS out plus GS back.

Point of equal time

The point where time to destination equals time back to departure; distance from departure equals total distance times GS out divided by the sum of the two ground speeds.

Leg fuel calculation

Leg fuel equals leg time in hours multiplied by fuel flow; leg time equals leg distance divided by ground speed, and reserves are added to the trip fuel.

UTC

Coordinated Universal Time, the reference time for aviation, based on atomic time and kept within 0.9 second of UT1 by leap seconds; all flight plans use UTC.

Local mean time

LMT equals UTC plus longitude divided by 15 hours, with east positive and west negative; 15 degrees of longitude corresponds to one hour of time difference.

Standard time zone

A region using UTC plus a fixed offset, usually a whole hour but sometimes half or quarter hours; boundaries follow political borders rather than meridians.

International date line

The line near 180 degrees longitude where the date changes; crossing eastward subtracts one day and crossing westward adds one day.

Rhumb line course formula

The tangent of the course equals departure divided by change of latitude; for long legs use meridional parts in Mercator sailing to find the course and distance.

Great circle distance formula

The cosine of the angular distance equals sine lat1 sine lat2 plus cosine lat1 cosine lat2 cosine of the change of longitude; multiply degrees by 60 for nautical miles.

GNSS trilateration

A receiver computes position from the measured travel times of signals from at least four satellites, resolving three position coordinates and the receiver clock bias.

RAIM

Receiver Autonomous Integrity Monitoring checks for faulty satellite signals using redundant measurements; it needs extra satellites in view and provides a warning when integrity is lost.

RNAV

Area navigation allowing flight on any desired path using VOR/DME, DME/DME, GNSS or inertial inputs, rather than routing directly over ground-based stations.