Navigation — Finding Your Way Across the Sky

Lesson 1 — True Course to Compass Heading: The TVMDC Conversion

Every cross-country flight starts with a line drawn on a chart. That line gives you a true course — measured from geographic north. But your aircraft's heading indicator and compass work from magnetic north, and your compass itself has additional errors. Before you can fly the course, you must convert it through a series of corrections.

The conversion sequence is TVMDC — a mnemonic remembered as "True Virgins Make Dull Companions." Working left to right converts chart course to what you dial into the cockpit. Working right to left reverses it.

Step 1 — True Course (TC)

True course is the direction of your intended path measured clockwise from true (geographic) north. You measure it from a sectional chart using a plotter aligned to the nearest meridian (line of longitude). Meridians run true north-south, so aligning your plotter to one gives a true measurement. True course doesn't change with location — it's a fixed geometric angle between your departure and destination.

Step 2 — Magnetic Variation (V): "East is Least, West is Best"

Magnetic variation is the angular difference between true north and magnetic north at a specific location. Magnetic north is currently located in northern Canada — not at the geographic North Pole — so compass needles across the US point in slightly different directions from true north depending on where you are.

Variation is depicted on sectional charts as isogonic lines — dashed magenta lines connecting points of equal variation, labeled with their value and direction (e.g., "12°W"). The agonic line (zero variation) runs roughly through the eastern Mississippi Valley. East of it: easterly variation. West of it: westerly variation.

The rule: East is Least, West is Best. Subtract easterly variation, add westerly variation when converting TC to MC.

Step 3 — Magnetic Course (MC)

Magnetic course is what your compass would read if it had no local errors. It accounts for the difference between true and magnetic north but not for the aircraft's own magnetic interference. In some parts of the US, variation is substantial — in Seattle it's about 16°E; in Maine it's about 16°W. Flying coast to coast requires applying very different variations.

Step 4 — Deviation (D): The Compass Correction Card

Every aircraft has its own magnetic personality. The engine, wiring, avionics, and metal structure create a local magnetic field that deflects the compass needle slightly from magnetic north. This error — called deviation — is different for every aircraft and varies with heading. A Cessna 172 on a heading of 360° might have 2° of easterly deviation, while on a heading of 180° it might have 3° of westerly deviation.

The deviation correction card is mounted on or near the compass in the cockpit. It lists the compass correction needed for various magnetic headings, usually in 30° increments. You read the card for the heading nearest your magnetic course and apply the correction.

Step 5 — Compass Heading (C)

Compass heading is what you set on your heading indicator (DI) and what you physically fly. It's the magnetic course corrected for deviation — the number that, when you hold it precisely, actually tracks you along your intended route.

Lesson 2 — Reading the Sectional Chart

The VFR sectional aeronautical chart is your primary navigation document. Published at a scale of 1:500,000 (one inch equals approximately 6.86 nautical miles), each chart covers about 340 × 340 miles and is updated every 56 days. Using an outdated chart for navigation is a FAR violation — always verify your charts are current before flight. See our sectional chart reading guide →

📷 Illustration · M06-IMG-02

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Airport symbols — the most important marks

Every airport on the chart has a symbol whose color and fill pattern tell you critical information before you even look at the data block.

The airport data block — decoded

Every charted airport has a data block adjacent to its symbol. Reading top to bottom, you'll find: airport name, elevation in feet MSL, control tower frequency (if towered, prefixed "CT-"), ATIS/ASOS frequency (if available, prefixed "A" or "A*" for ASOS), longest runway length in hundreds of feet (70 = 7,000 ft), and UNICOM frequency. A star (*) next to the elevation indicates pilot-controlled lighting. An "L" indicates the airport has runway lighting.

Maximum Elevation Figures (MEF)

Scan your sectional and you'll see large blue numbers — typically 4 to 5 digits — sitting in the middle of each latitude/longitude quadrant. These are Maximum Elevation Figures (MEF). They represent the height of the highest known terrain or obstacle in that quadrant, rounded up to the next 100 feet and then increased by an additional 100 feet of buffer. Flying at or above the MEF provides clearance from all charted obstacles in that quadrant.

Isogonic lines and measuring true course

The dashed magenta lines you see crossing the chart diagonally are isogonic lines — connecting points of equal magnetic variation. When measuring true course with your plotter, align the plotter to the nearest meridian. The angle between the meridian and your course line is the true course. Then apply the variation shown by the nearest isogonic line to convert TC to MC.

Distance measurement: one degree of latitude equals exactly 60 nautical miles. The latitude scale printed on the left and right margins of the sectional chart can be used directly as a nautical mile scale — simply transfer with your plotter. One minute of latitude = one nautical mile.

VOR compass roses

VOR stations on the chart appear as hexagons surrounded by a compass rose. The compass rose shows magnetic bearings from the VOR station — it is already corrected for local variation. When you see a VOR compass rose, you can visually estimate which radial you would be on from any position on the chart. This quick situational awareness check is valuable during cross-country navigation.

Lesson 3 — Pilotage and Dead Reckoning

Before GPS, before VORs, pilots navigated using two fundamental techniques: pilotage (looking out the window and matching the ground to the chart) and dead reckoning (calculating where you must be based on where you started, how fast you went, and for how long). Today, both remain essential skills — required on your checkride, and more reliable than electronics when technology fails.

Pilotage — navigating by visual landmarks

Pilotage is navigation by visual reference to ground features identified on the chart. The technique requires discipline and a methodical approach. Effective pilotage pilots:

• Pre-select checkpoints before the flight — choose features that are unmistakable from the air. A large lake is better than a pond. A freeway interchange is better than a country road. A prominent hill is better than a gentle rise. Space checkpoints 15–25 nm apart so you're checking position every 10–15 minutes at cruise speed.
• Identify two features simultaneously at each checkpoint. Single-feature identification is risky — similar features exist throughout the country. A river and a highway crossing it, confirmed together, is much more reliable than either alone.
• Look ahead, not just down. As you approach a checkpoint, orient yourself to what the chart shows should be visible ahead of you. Matching a panoramic view to the chart is faster than searching for a single feature directly below.
• Don't rationalize.} If the ground doesn't match the chart at your checkpoint, you are not where you think you are. Stop rationalizing features into matching and identify your actual position before continuing.

Dead reckoning — calculating position mathematically

Dead reckoning (DR) calculates current position from a known starting point by applying your heading, true airspeed, time elapsed, and wind correction. It is the basis of the navigation log (nav log) you complete before every cross-country.

The core DR relationship: Distance = Groundspeed × Time. Rearranged: Time = Distance ÷ Groundspeed, or Groundspeed = Distance ÷ Time. If you know any two, you can solve for the third.

Combining pilotage and DR produces more reliable navigation than either technique alone. Fly dead reckoning between checkpoints, then use pilotage to confirm your position at each checkpoint. If your dead reckoning ETA and your pilotage position agree — you're on track. If they diverge, investigate before continuing.

Lesson 4 — VOR Navigation

VOR (VHF Omnidirectional Range) is a ground-based navigation aid that broadcasts on VHF frequencies between 108.0 and 117.95 MHz. VOR stations transmit 360 magnetic radials — bearings measured FROM the station — which properly equipped aircraft receivers detect and display. VORs remain valuable navigation aids even in the GPS era, and VOR interpretation is tested on every Private Pilot written exam.

How the VOR system works

Each VOR transmits two signals simultaneously: a reference phase signal broadcast in all directions, and a rotating directional signal. The phase difference between the two signals at the aircraft's location corresponds directly to the magnetic bearing from the VOR to the aircraft. Your VOR receiver processes this phase difference and displays it on the CDI (Course Deviation Indicator).

VOR identification is broadcast as a Morse code signal (and sometimes voice) on the VOR frequency. You must positively identify a VOR before navigating by it — this means listening for and recognizing its 3-letter Morse code identifier. Never navigate on a VOR you haven't identified. If the station is under maintenance, the identifier will be absent or replaced with the letters "T-E-S-T" — do not navigate on it.

Using the VOR CDI — step by step

The VOR instrument has three moving parts: the OBS (Omni-Bearing Selector, the knob you turn), the CDI needle (the vertical line that deflects left or right), and the TO/FROM flag (showing whether the selected course takes you toward or away from the station).

To determine your position from a VOR: Tune and identify the VOR. Slowly rotate the OBS until the CDI centers with a FROM flag — the number in the OBS window is your radial (your bearing FROM the station). If the CDI centers with a TO flag, you are on the reciprocal — add or subtract 180°.

To navigate TO a VOR: Tune and identify. Rotate the OBS until you get a TO flag with the CDI roughly centered, setting your desired inbound course. Fly to keep the CDI centered. When the needle deflects, turn toward the needle — fly toward where the needle is pointing, not away from it. Each dot of deflection typically represents 2° of course error.

VOR limitations

VOR accuracy is ±1° under ideal conditions, but degrades with distance and terrain. VORs have published service volumes — the ranges within which reception is guaranteed at specific altitudes. Terminal VORs (T) serve within 25 nm, Low Altitude VORs (L) within 40 nm below 18,000 ft, and High Altitude VORs (H) within 100 nm at higher altitudes. Using a VOR beyond its service volume is unreliable and not recommended for navigation.

Lesson 5 — E6B Flight Computer Calculations

The E6B flight computer is a circular slide rule that solves the most common pilot math problems without electricity. You are required to know how to use it for your written test and practical test. Modern EFBs and apps do these calculations automatically — but understanding the underlying math makes you a better pilot and is tested on every written exam.

Time-Speed-Distance (TSD)

The fundamental relationship: Distance = Speed × Time. On the E6B, the rate index (marked "60" on the outer ring) is the pivot point for TSD problems. Set your known rate (groundspeed) on the outer ring against the rate index (60), then read time opposite any distance on the inner ring, or distance opposite any time.

Fuel calculations

Fuel calculations use the same TSD scale — just substitute fuel flow rate (gallons per hour) for speed and gallons for distance. The relationship: Fuel Used = Flow Rate × Time.

True airspeed (TAS) from indicated airspeed (IAS)

TAS increases approximately 2% per 1,000 ft above sea level because the air is less dense and the aircraft moves through it faster for the same IAS. The E6B wind side calculates exact TAS from pressure altitude and temperature: align the pressure altitude with the temperature in the airspeed window, then read TAS opposite IAS on the circular scales.

Quick mental approximation: at 8,000 ft pressure altitude, TAS ≈ IAS × 1.16 (16% higher than indicated). At 10,000 ft, TAS ≈ IAS × 1.20.

Wind correction angle (WCA) and groundspeed

Wind pushes the aircraft sideways and either adds to or subtracts from your groundspeed depending on direction. The wind side of the E6B (the circular grid) solves for the wind correction angle (how much to offset your heading into the wind to maintain course) and the resulting groundspeed.

The method: plot the wind direction and speed on the wind side, rotate the grid to your true course, and slide the grid to align with TAS. The wind correction angle reads directly off the grid, and the groundspeed appears at the grommet. This is a mechanical process — practice it several times before your written test until it's automatic.

Lesson 6 — GPS in VFR Operations

GPS has transformed general aviation navigation. The Global Positioning System provides continuous, accurate position information to any aircraft with a GPS receiver. For VFR pilots, GPS is simultaneously the most useful navigation tool available and — if over-relied upon — one of the most dangerous.

How GPS works

GPS receivers calculate position by measuring the time it takes signals from multiple satellites (at minimum 4 for a 3D position fix) to arrive. Each satellite broadcasts its position and a precise timestamp. The receiver calculates the distance to each satellite and triangulates position to within a few meters under normal conditions. The US GPS constellation consists of 31 operational satellites in medium Earth orbit, providing global coverage.

GPS for VFR — the critical limitation

For VFR flight, GPS is classified as supplemental navigation — it is not FAA-approved as a sole means of navigation. The practical implication: always have a backup navigation method. A VFR cross-country should be planned with pilotage checkpoints and dead reckoning regardless of whether you have GPS. GPS databases can be outdated (airport data, airspace boundaries, and obstacles change), GPS signals can be jammed or spoofed, and receivers can fail.

RAIM — Receiver Autonomous Integrity Monitoring

RAIM is the GPS receiver's built-in self-monitoring function. It uses the geometry of available satellite signals to assess whether the position solution has sufficient accuracy and integrity for navigation. When RAIM is unavailable (too few satellites in useful geometry, or a satellite has been excluded due to a fault), the receiver alerts the pilot that the GPS position cannot be trusted for navigation.

For VFR flight, RAIM is less critical than for IFR — the visual references outside provide position confirmation. For IFR GPS approaches, RAIM availability at the time of approach must be confirmed during preflight planning. If RAIM is predicted to be unavailable during the approach, an alternate approach method must be planned.

GPS database currency

IFR-certified GPS units require regular database updates (typically every 28 days following the AIRAC cycle) to remain approved for instrument approaches. VFR GPS units have no legal database currency requirement, but using outdated data is unsafe — airports close, airspace boundaries change, and new obstacles are erected. Treat your GPS as you would a sectional chart: verify currency before relying on it.

Lesson 7 — Planning a Complete VFR Cross-Country

A complete cross-country flight plan integrates everything in this module: chart reading, TVMDC conversion, pilotage checkpoints, dead reckoning calculations, E6B math, and weather awareness. Here is the complete sequence, step by step.

Step 1 — Select your route

Draw a direct line from departure to destination on your sectional. Check for obstacles along the route — is the direct course over mountains or terrain requiring a specific altitude? Does it penetrate restricted airspace or MOAs? Are there TFRs? If the direct route has issues, plan a dogleg around them. Note 4–6 prominent landmarks along the route for pilotage checkpoints, spaced 15–25 nm apart.

Step 2 — Measure true course and distance

Using your plotter, align to the nearest meridian and read the true course for each leg. Measure distance directly on the chart using the latitude scale (1° = 60 nm, 1' = 1 nm) or your plotter's distance scale.

Step 3 — Convert to compass heading (TVMDC)

Apply the magnetic variation from the nearest isogonic line to convert TC to MC. Read the deviation from the compass correction card for the MC heading to get compass heading. Record all three (TC, MC, CH) on your nav log.

Step 4 — Obtain winds aloft forecast and calculate WCA/GS

Get the winds aloft forecast for your route from 1800wxbrief.com. Winds aloft are given in true direction and knots. Use the E6B wind side to calculate wind correction angle and groundspeed for each leg. Note: winds aloft are in true degrees — apply variation to convert to magnetic WCA before adding to MC to get magnetic heading.

Step 5 — Calculate fuel and ETAs

Using the calculated groundspeed, E6B TSD: time per leg = distance ÷ groundspeed. Sum all leg times for total flight time. Multiply by fuel burn rate (from POH performance charts at your planned altitude and power setting) for enroute fuel. Add required reserves (30 min day VFR, 45 min night VFR minimum — more if practical). Verify against usable fuel on board.

Step 6 — Weather briefing

Get a full standard briefing from 1800wxbrief.com — not just an app check. Review: current conditions along the route (METARs), forecast at departure, destination, and alternates (TAFs), winds aloft, AIRMETs and SIGMETs, NOTAMs for all airports and the route, and TFRs.

Step 7 — File and open the flight plan

File a VFR flight plan — not legally required but strongly recommended. After takeoff, open the flight plan with FSS. After landing, close it immediately — or a search will begin 30 minutes after your estimated arrival time. An open, unclosed flight plan is a serious matter that activates search and rescue resources unnecessarily.