DGCA CPL Air Navigation cheat sheet

Earth is an oblate spheroid: equatorial radius about 6378 km, polar radius about 6357 km, flattening about 1/297.

A great circle is the shortest surface path between two points; its plane passes through Earth's centre, and it bisects every other great circle.

A rhumb line cuts every meridian at the same angle; it plots as a straight line on a Mercator chart but is longer than a great circle except on the equator or a meridian.

One minute of latitude equals 1 NM (1.852 km); departure in NM equals change of longitude in minutes multiplied by cos(latitude).

LMT = UTC + east longitude/15 or UTC − west longitude/15; 15° of longitude equals 1 hour and 1° equals 4 minutes.

Magnetic bearing = true bearing − easterly variation (+ westerly variation); compass heading = magnetic heading − easterly deviation (+ westerly deviation).

Magnetic dip is zero at the magnetic equator and 90° at the magnetic poles; compass turning errors are greatest in high magnetic latitudes.

Isogonal lines connect points of equal magnetic variation; the agonic line is the line of zero variation.

Crossing the International Date Line westward adds one day; crossing it eastward subtracts one day, subject to local political boundaries.

Mercator projection is conformal; rhumb lines are straight, while great circles plot as curves that bulge poleward and are not straight lines.

Lambert conformal conic charts are conformal, have scale correct on the standard parallels, and show straight lines that closely approximate great circles.

Polar stereographic charts are used for polar regions; meridians are straight lines radiating from the pole and great circles are nearly straight.

A representative fraction of 1:500,000 means one unit on the chart represents 500,000 of the same units on Earth; 1 cm equals 5 km.

One-in-sixty rule: track error in degrees = 60 × off-track distance / distance flown; closing angle = 60 × remaining offset / distance remaining.

Wind triangle: ground speed = TAS × cos(drift) plus the along-track wind component; approximate ground speed = TAS ± headwind or tailwind component.

Wind correction angle: sin(WCA) = (wind speed × sin(wind angle to track)) / TAS; for small angles, WCA ≈ 60 × crosswind component / TAS.

Fuel required = (distance / ground speed) × fuel flow + reserves; endurance = usable fuel / fuel flow.

QNH makes the altimeter indicate elevation above mean sea level; QFE reads zero at the reference point; QNE is 1013.25 hPa for flight levels; in colder-than-ISA air, true altitude is lower than indicated altitude.

ADF magnetic bearing to station = magnetic heading + relative bearing, with 360° subtracted or added as needed; relative bearing 0° means the station is ahead.

ADF errors include night effect, coastal refraction, mountain effect, precipitation static, and quadrantal error; the sense antenna resolves the 180° ambiguity.

VOR operates in the 108.0–117.95 MHz band, is line-of-sight, and provides magnetic radials from the station; the CDI shows deviation from the selected radial and the TO/FROM flag shows direction.

An aircraft on the 090 radial is east of the VOR; to fly inbound to the station on that radial, select 270° with a TO indication.

DME measures slant range in nautical miles, is frequency-paired with VOR or ILS, and has accuracy of about ±0.5 NM or 3% of range; groundspeed is derived from range change.

ILS localizer operates in the 108–112 MHz band and provides lateral guidance using 90 Hz left and 150 Hz right modulation; the glideslope operates in the 329–335 MHz band and is typically 3°.

ILS marker beacons: outer marker about 4–7 NM from the threshold, middle marker about 3500 ft from the threshold, and inner marker close to the threshold; each gives a distinct aural tone and light.

Secondary surveillance radar interrogates at 1030 MHz and receives replies at 1090 MHz; Mode A gives identity, Mode C gives altitude, and codes 7500, 7600, and 7700 indicate hijack, radio failure, and emergency.

GNSS pseudorange equals the speed of light multiplied by signal travel time; at least four satellites are needed for a three-dimensional position and time solution.

RAIM uses redundant satellite measurements to detect and exclude faulty signals; five satellites are needed for fault detection and six for fault exclusion.

Dilution of precision describes how satellite geometry amplifies ranging error; lower HDOP, VDOP, PDOP, or GDOP values indicate better geometry and accuracy.

SBAS, such as WAAS or EGNOS, broadcasts wide-area corrections and integrity data from geostationary satellites; GBAS provides local corrections and integrity monitoring near an airport.

RNAV permits point-to-point navigation using VOR/DME, GNSS, or inertial systems; RNP adds on-board performance monitoring and alerting within a defined containment volume.

PBN navigation specifications include RNAV 10, RNAV 5, RNAV 2, RNAV 1, RNP 4, RNP 2, RNP 1, and RNP 0.3; the number denotes required navigation accuracy in nautical miles.

ADS-B Out broadcasts aircraft position, velocity, and identity; ADS-B In receives traffic and weather; common datalinks are 1090ES and UAT.

An inertial navigation system uses accelerometers and gyroscopes, is self-contained, drifts over time, and requires alignment before flight.

TCAS interrogates nearby transponders and issues traffic advisories and resolution advisories; a resolution advisory commands a vertical escape manoeuvre.