Key notes — quick revision

061 General NavigationQuick revision

Use this page for last-minute revision. For full explanations and diagrams, read chapters 1–4.

Solar system & earth

Key fact

Midnight sun — sun visible 24 h. Polar circles 66.5°N/S. Cancer/Capricorn 23.5°N/S. Perihelion Jan, Aphelion Jul.

Key fact

Sidereal day — constant, star reference. Apparent solar day — varies (elliptical orbit + axis tilt). Solar day > sidereal day.

Key fact

1-in-60 — small angles only. Convergence = Δlong × sin lat. Conversion angle = ½ Δlong × sin lat. Departure = 60 × cos lat (per degree form in notes) / Δlong × cos lat.

Key fact

Halfway between two points: GCT = RLT (great circle track = rhumb line track at mean meridian). Initial RLT reciprocal of final RLT.

Time

Key fact

UTC = LMT ± (long × 4 min). Watch daylight saving. 1200 LMT → mean sun hour angle 000°. Air almanac times in LMT; max time diff 13 h.

Key fact

Civil twilight — sun centre 6° below horizon. Twilight longer at high latitudes. Equation of time max Feb & Nov.

Key fact

S.E.A. — September equinox autumn. M.E.S. — March equinox spring. Solstice — Jun (summer) / Dec (winter).

Magnetism & grid

Key fact

Magnetic variation max 180°. West = (−), East = (+) in many conventions. Agonic — zero variation. Isogrivs — equal grivation.

Key fact

Grivation = grid convergence + variation. Grid convergence westerly — TN west of GN (E of datum, NH). Purpose of grid — constant direction where GC would otherwise curve.

Exam trap

ANDS (NH) / UNOS (SH) for turning errors. Turning: N/S. Acceleration: E/W. Undershoot north when turning (NH).

Charts

Key fact

Mercator: scale ∝ sec lat, convergency 0, straight line = RL. Lambert: scale min at PO, straight ≈ GC, CC = Δlong × sin PO. Polar stereo: scale min at pole, plane projection.

Key fact

Conformal — scale equal in parallel & meridian directions over short distance; meridians ⊥ parallels. Large scale = small area, good detail.

Navigation & DR

Key fact

Drift FROM heading TO track. DR on desired track. GS² = TAS² + W² − 2×TAS×W×cos(wind angle). Min ISA −56.5°C at FL360+.

Key fact

TAS from IAS (standard): ~+2% per 1000 ft + temp correction. Compressibility ~0.95 at FL290. 3° glideslope ROD ≈ GS × 5.

Key fact

TKE = WCA (track error angle equals wind correction angle in cruising nav). Total track correction = TKE along track + TKE to go.

Mnemonics & exam habits

Key fact

Read question AND answers first. Note (M) vs (T) wind, CAS vs TAS. Whiteout — snow, horizon blends with sky. Two parallel roads at right angles — can determine GS.