How do you fill out a nav log for a cross-country flight?

For each leg: measure the true course and distance on the chart, solve the wind triangle with your TAS and the forecast winds aloft to get wind correction angle and groundspeed, apply magnetic variation (and compass deviation) to get the heading to fly, then compute leg time from distance and groundspeed and fuel from time and burn rate. Chain the leg times from your departure time for ETAs, and total the distance, time, and fuel.

Should each leg use different winds aloft?

Yes, when the route is long enough to cross different forecast points or altitudes. Winds aloft forecasts are published for specific stations and altitudes; use the forecast nearest each leg. On short trips one wind entry is usually fine, and this planner lets you set winds per leg either way.

Do I add variation or subtract it?

East is least, west is best: subtract easterly variation from true heading, add westerly. A 289° true heading with 17° east variation is a 272° magnetic heading. Enter easterly variation as a negative number in this planner and it handles the sign for every leg.

Cross-Country Trip Planner: Headings, Leg Times & Fuel

Aircraft & route constants

True airspeed (kt)

From the TAS calculator or POH

Fuel burn (GPH)

Magnetic variation (°)

West positive, east negative

Compass deviation (°)

From the deviation card (optional)

Departure time

Local or Zulu; ETAs use the same clock

Legs

Nav log

Leg	CHdg	GS	ETE	ETA	Fuel

Add legs to build the nav log.

A nav log is the wind triangle solved once per leg, chained in time. Each leg turns distance, true course, TAS, and the winds aloft into a magnetic heading, a groundspeed, a leg time, and a fuel burn; the departure time threads them into ETAs. This planner does what an E6-B or CX-3 trip function does, with every leg visible at once. Your entries stay on this device.

What happens on each line

Every leg runs the same five steps a flight computer does:

Wind correction angle = arcsin(wind speed × sin(wind direction − course) ÷ TAS). This is the crab that keeps your track on the course line.
True heading = course + WCA, then magnetic heading = true heading + westerly variation (subtract easterly), then compass heading adds deviation. "True Virgins Make Dull Company": True, Variation, Magnetic, Deviation, Compass.
Groundspeed = TAS × cos(WCA) − wind speed × cos(wind direction − course).
Leg time = distance ÷ groundspeed; each leg's ETA becomes the next leg's start.
Fuel = burn rate × leg time; the totals row is your minimum fuel requirement before reserves.

Add your reserve on top with the fuel & endurance calculator: the trip total here plus 30 to 60 minutes at cruise burn is the number that has to fit in your tanks.

How pilots use a trip plan

Plan the night before, with forecast winds. The headings column goes on your kneeboard; the groundspeed column is what you will verify in flight.
Fly the first leg as a test. Time yourself between checkpoints; if measured groundspeed disagrees with the planned column, every later ETA and the fuel total move with it. Renegotiate early.
Watch the totals, not just the legs. A trip that is fine leg-by-leg can still land you with less fuel than your personal minimum after a slow first hour. The totals row is the go/no-go number.
Student tip: checkride examiners want to see this table built by hand at least once. Build it here, then verify one leg with your E6-B so you can show the work.

The worked example (a real CX-3 manual problem)

A Cessna 172 (110 kt TAS, 9.5 GPH, 17° east variation, 0° deviation) flies Renton (KRNT) → Forks (S18) → Ocean Shores (W04) → back to KRNT, departing 12:00:00Z. Load it with the button above:

Leg 1: 92.3 NM, course 288°, wind 350° at 3 kt → GS 109 kt, 51:00, ETA 12:51:00
Leg 2: 57.3 NM, course 170°, wind 200° at 6 kt → GS 105 kt, 32:49, ETA 13:23:49
Leg 3: 84.2 NM, course 069°, wind 140° at 5 kt → GS 108 kt, 46:40, ETA 14:10:29
Totals: 233.8 NM, 2:10:29 enroute, 20.7 gallons

Those are the same answers the flight-computer manual publishes, to the second.

Common Questions

Where do the distances and courses come from?

From the sectional chart with a plotter, or from your EFB's route view. Measure the true course (against a meridian, not the compass rose of a VOR) and the distance of each straight segment between checkpoints. Turn points are where the course changes, and each one starts a new leg.

Why is my groundspeed different on the reciprocal leg home?

The wind that slowed you outbound helps you home, but not symmetrically: the crosswind portion costs groundspeed in both directions (you crab both ways), so a round trip in wind always takes longer than the same trip in calm air. Never plan a round trip assuming the tailwind gives back what the headwind took.

Does this replace a flight plan or a briefing?

No. It builds the arithmetic layer of a nav log: headings, times, and fuel. You still need a weather briefing, NOTAMs, performance and W&B checks, and, if you want search-and-rescue coverage, a filed flight plan. The go/no-go framework covers how the pieces fit together.

Related tools and guides

True Airspeed Calculator

The TAS constant this planner needs, from CAS, altitude, and temperature.

Fuel Burn & Endurance Calculator

Check the trip's fuel total against your tanks and reserve.

Weight & Balance Calculator

The other half of the preflight math: loading and CG.

Planning is half the decision

FlightDecide checks the weather, NOTAMs, fuel, performance, and W&B for your specific route and window, scores it GO, CAUTION, or NO GO, and shows the raw data behind every call.

Get FlightDecide on the App Store

Educational tool for flight-planning practice. It is advisory only and not a substitute for your POH, an official weather briefing, or your own judgment as pilot in command (14 CFR 91.3). Sources: FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Ch. 16. Last reviewed: July 17, 2026.