ATPL Navigation flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Oblate spheroid
- The Earth's shape, flattened at the poles and bulging at the equator; equatorial radius 6378.1 km, polar radius 6356.8 km, flattening about 1/298.3.
- Great circle
- A circle on the Earth's surface whose plane passes through the Earth's centre; it is the shortest path between two points and its track changes continuously.
- Rhumb line
- A line that crosses every meridian at the same angle, giving a constant track; it is longer than the great circle except on the equator or a meridian.
- Departure formula
- Departure in nautical miles equals change of longitude in minutes multiplied by the cosine of the latitude; it gives the east-west distance along a parallel.
- Magnetic variation
- The angle between true north and magnetic north at a place; easterly variation is subtracted from true bearing to obtain magnetic bearing.
- Compass deviation
- The angle between magnetic north and the compass north of a particular aircraft installation, caused by aircraft magnetic fields and electrical circuits.
- Agonic line
- The line joining points of zero magnetic variation; crossing it means the magnetic and true meridians coincide at that position.
- Northerly turning error
- A compass error during turns in the Northern Hemisphere; the compass lags or leads in turns from north or south, largest at high latitude.
- Flux valve
- A remote-reading compass component that senses the horizontal component of the Earth's magnetic field and supplies signals to slave the directional gyro.
- Mercator projection
- A cylindrical, conformal chart projection on which rhumb lines are straight and scale increases with latitude; great circles appear curved.
- Lambert conformal conic
- A conformal conic projection using standard parallels; meridians are straight and converging, and great circles plot approximately as straight lines.
- Chart scale
- The ratio of a chart distance to the corresponding ground distance, expressed as a representative fraction such as 1:500,000.
- Isogonal line
- A line on a chart joining points of equal magnetic variation; it shows how variation changes across the area covered.
- Triangle of velocities
- A vector diagram combining heading and true airspeed with wind velocity to give track and ground speed; the basis of dead reckoning.
- Wind correction angle
- The angle between heading and track needed to counter drift; sin(WCA) equals wind speed times sine of wind angle divided by TAS.
- Drift
- The angle between the aircraft's heading and its actual track over the ground, caused by the wind; positive drift means track is right of heading.
- Ground speed
- The speed of the aircraft over the ground, equal to the along-track component of true airspeed plus the wind component along track.
- 1-in-60 rule
- A rule of thumb stating that a 1 degree angular error produces a 1 NM offset after 60 NM; useful for quick track-error corrections.
- Lost procedure
- Actions when uncertain of position: maintain heading and altitude, note the time, use radio aids and ATC, and climb if safe to improve range.
- Visual fix
- A position determined by matching chart features with ground landmarks; two or more lines of position give a reliable fix.
- Relative bearing
- The angle measured clockwise from the aircraft's nose to the direction of a radio station; magnetic bearing equals heading plus relative bearing.
- VOR radial
- The magnetic bearing from a VOR station to the aircraft; it is displayed as the selected course and indicated by the CDI and TO/FROM flag.
- DME slant range
- The line-of-sight distance from the aircraft to the DME station; ground distance equals the square root of slant range squared minus altitude squared.
- ILS localizer
- The lateral guidance component of an ILS, transmitting on 108-112 MHz and providing course deviation to the runway centreline.
- RAIM
- Receiver autonomous integrity monitoring; a GNSS function that detects and, with sufficient satellites, isolates faulty signals to warn of integrity failures.
- RNP
- Required navigation performance; a navigation specification requiring onboard performance monitoring and alerting, with an accuracy value expressed in nautical miles.
- Navigation database
- The FMS store of waypoints, airways, navaids, and procedures in ARINC 424 format; it must be current and matched to the flight plan.
- Fly-by waypoint
- A waypoint at which the aircraft begins the turn toward the next leg before reaching the waypoint, smoothing the flight path.
- VNAV
- The FMS vertical navigation mode that follows altitude and speed constraints and computes climb, cruise, and descent profiles.
- Grid navigation
- A polar navigation method using grid north referenced to the Greenwich meridian, because the magnetic compass is unreliable near the poles.
- Great-circle planning
- Route planning along the shortest path between two points, using spherical trigonometry; track changes continuously along the route.
- Convergence
- The angle between meridians, increasing toward the poles; it determines the difference between true track and grid track on polar charts.