EASA PPL Navigation (P90) — Study Guide

Navigation is where conceptual understanding, chart reading, and calculation converge — one question can blend wind correction, heading conversions, timing, and awareness checks. The P90 exam is commonly 20 questions · 60 minutes · 75% (15/20), sharing the longer slot with papers like Meteorology and Flight Performance & Planning. Build the triangle of velocities mental model once and reuse it everywhere.

The Earth and coordinates

Navigation treats Earth as a sphere (actually oblate). Equatorial circumference ≈ 40 000 km ≈ 21 600 NM ⇒ 1° latitude ≈ 60 NM and 1′ latitude = 1 NM — foundational for chart measurement.

Latitude — angular distance north/south of equator along parallels. Longitude — east/west of Prime Meridian; meridians converge poleward ⇒ east-west ground distance per minute of longitude shrinks by cos(latitude) versus equator.

Great circles vs rhumb lines

A great circle is shortest surface path between points (meridians + equator are examples). A rhumb line cuts meridians at constant bearing — convenient mentally when flying constant headings.

On typical European VFR Lambert charts straight segments approximate practical navigation over PPL distances; Mercator straight lines are rhumb lines with scale distortion increasing toward poles — always measure east-west distances on the latitude scale at your working latitude.

Charts and projections

Mercator

Cylindrical, conformal (angles true locally). Rhumb lines plot straight — handy for oceanic constant-heading mental maths but latitude stretches scale north/south.

Lambert conformal conic

Standard for many ICAO 1:500 000 VFR charts — conformal with manageable distortion across chart bands; meridians converge as on Earth.

Scale 1:500 000 ⇒ 1 cm = 5 km ground — verify with printed latitude ticks + navigation plotter rather than guessing bar scales alone.

Magnetism and compasses

Variation

Angle between true north and magnetic north at a place — labelled East/West on charts. Example (westerly variation): True to Magnetic: add west (variation west, magnetic best); reverse when going magnetic → true.

Deviation

Aircraft magnetic errors from structure/electrics — unique per airframe/heading; recorded on a deviation card after compass swing.

Full mnemonic chain TVMDC ("True Virgins Make Dull Company") orders transforms between true, magnetic, and compass headings/bearings — practise both directions until automatic.

Triangle of velocities

Three vectors interlock: heading + TAS (through air), wind vector (airmass motion over ground), yields track + groundspeed (path over Earth). Know any two ⇒ solve the third (computer or sketch).

Wind from the left ⇒ generally crab heading left into wind to maintain planned track — examiners verify vector sense, not only arithmetic.

1-in-60 rule

Approximately: 1 NM offset at 60 NM range ≃ 1° track error angle. Track error = (distance off ÷ distance flown since fix) × 60°; closing angle = (distance off ÷ distance to go) × 60°. Many scenarios require both portions — correcting only track error leaves you parallel but still displaced.

Navigation computer

Circular slide rules solve wind triangles, TAS from RAS/CAS + altitude/temperature, fuel/time — exam pace rewards fluent technique; electronic equivalents acceptable if permitted — confirm with your invigilator guidelines.

True vs indicated airspeed

ASI senses dynamic pressure ⇒ density couples into indication. Same TAS at altitude shows lower IAS. Rule of thumb (ISA-ish): TAS roughly ~2% higher than CAS per 1 000 ft — enough for sanity checks when interpolating exam tables.

CAS refines IAS for instrument/position error using AFM corrections — small at cruise on trainers but quoted on performance graphs.

Flight planning

Plot legs waypoint-to-waypoint with true tracks, convert through variation → magnetic, apply wind correction ⇒ magnetic heading, deviation ⇒ compass heading.

Choose bold ground features — ambiguous copse-level fixes fail under stress. Record a structured PLOG: legs, distances, headings, GS, times, fuel — exams supply partial PLOGs to complete.

ETA discipline: time = distance ÷ groundspeed — compare observed fixes vs plan; early/late signals wind errors or heading drift.

En-route techniques

• Map reading — continuous timeline expectation ("next feature at x minutes") beats frantic scanning.
• Lost protocol mindset — stop worsening drift (usually fly planned heading briefly), gain big picture features, confirm with second cue, inform ATC when sensible.
• DR navigation — integrates headings/times/winds to estimated position until a visual fix confirms — errors accumulate; reset often.

Radio navigation aids (overview)

VOR

VHF omni-range gives magnetic bearing state via phase comparison — CDI centers on selected radial; line-of-sight range grows with altitude — understand OBS/CDI failure modes conceptually.

NDB / ADF

ADF relative bearing clockwise from nose — convert to magnetic bearing to station with Mag bearing = Mag heading + relative bearing (subtract 360 if needed). Expect exam mentions of coastal bending, night effects, and thunderstorm attraction of needles.

GPS

Excellent supplementary navigation — exams still expect retained chart/backup proficiency; understand integrity concepts (mask angle, outage, database currency at overview level).

Where students lose marks

• TVMDC direction mistakes — rehearse westerly vs easterly variation alongside deviation card sign.
• 1-in-60 partial solutions — include closing angle when question demands converge on destination.
• Relative → magnetic bearing arithmetic under time pressure — drill carry/add/subtract 360 wrap.
• Using CAS/IAS as TAS at altitude — triangle answers drift wildly if density step skipped.

How to prepare

Timed integrated legs beat isolated facts — measure real chart segments, compute winds from forecasts, fill entire PLOGs, then debrief errors. 60-minute papers punish hesitation — automate mechanics so cognition stays for traps embedded in stems.