Learning hub · Flight Planning and Monitoring · Lesson 1

Flight planning: fuel, the navigation log and monitoring in flight

A good plan answers three questions before you start the engine: how long will it take, how much fuel do you need, and what will you do if it goes wrong? Then in the air you check the plan against reality and change it early. This lesson shows the method.

About 14 minutes, plus the quiz. Part of Flight Planning and Monitoring. It uses the sums from The wind triangle.

1. Fuel planning: the parts

The fuel you carry is made of separate parts. Each has a purpose. You add them up, and the sum must be less than the usable fuel in the tanks.

Taxi fuel. The fuel burned from engine start to the start of the take-off roll, including the run-up.
Trip fuel. The fuel from take-off to landing at the destination, including the climb, the cruise and the descent, with the wind and the routing you have planned.
Contingency fuel. An extra amount for the things that never go exactly to plan: a stronger headwind, a small detour, a longer wait for a clearance.
Alternate fuel. The fuel to fly from the destination to an alternate aerodrome, if one is needed because the weather or the destination might not allow a landing.
Final reserve fuel. The fuel you must still have in the tanks on landing. It is not for use in the plan. It is the last margin when everything else has gone wrong.

You may also carry extra fuel at your own discretion. More fuel gives more safety, but it also adds mass, so check the mass and balance.

This lesson teaches the idea only. The exact amounts and times required for your flight come from the regulation that applies (for private flights in Europe, the fuel requirements are in EASA Part-NCO, NCO.OP.125, and national rules may add to them; its acceptable means of compliance give a final reserve of 30 minutes at holding speed at 1,500 ft above the destination for day VFR, and 45 minutes at night, but check the current text), from your operator or flying school, and from your national authority. They differ with the type of aeroplane, the type of flight, and day or night. Find the current text and your school’s rules, and use the flight manual for the fuel flows. Never plan to use the final reserve.

2. A simple navigation log

A navigation log is a table with one row per leg of the route. It turns the chart into numbers that you can check in flight. For each leg you write:

the two points, the track (true or magnetic, as you are taught) and the distance in nautical miles;
the wind, the heading you must fly and the groundspeed, from the wind triangle (use the wind-triangle calculator to check your answer);
the time for the leg and the fuel for the leg;
blank spaces for the actual times and for the fuel in the tanks, filled in during the flight.

The sums are simple:

Time (min) = distance ÷ groundspeed × 60 Fuel (L) = time (h) × fuel flow (L/h)

The time and fuel calculator does these two sums for you. Use it to check, but learn to do the sums by hand.

3. A worked example

The aeroplane, the route and the numbers here are all invented. The groundspeeds are given, as if they came from the wind triangle. The aeroplane burns 28 litres per hour in the cruise, and its tanks hold 80 litres of usable fuel.

Leg	Distance (NM)	Groundspeed (kt)	Time (min)	Fuel (L)
A to B	30	90	20	9.3
B to C	44	110	24	11.2
C to D	27	90	18	8.4
Trip	101		62	28.9

Leg A to B: 30 ÷ 90 × 60 = 20 min and 20 ÷ 60 × 28 = 9.3 L. The other legs work the same way. The trip is 62 minutes and about 29 L.

Now the other parts. These amounts are also invented, to show the method. They are not the amounts any regulation requires and not a recommendation:

Taxi: 3 L.
Trip: 29 L (rounded up from 28.9).
Contingency: 10 per cent of the trip fuel, about 3 L.
Alternate: 12 minutes to the alternate at the same fuel flow, 12 ÷ 60 × 28 = 5.6, so 6 L.
Final reserve: 30 minutes at 28 L/h (for simplicity, the cruise fuel flow) = 14 L.

Total: 3 + 29 + 3 + 6 + 14 = 55 L. The tanks hold 80 L, so the flight is possible, with 25 L spare for extra margin. Notice that the 14 L final reserve is still in the tank at the end, and the flight must land with it. Also notice that you round fuel up, not down.

4. Monitoring the flight

The log is a prediction. In flight, you compare it with what is really happening, and you do it often.

Gross-error check. After take-off, and at each point, ask whether the position makes sense. Does the heading agree with the track on the chart? Does the sun, the coast or a big road or railway lie where the chart says it should? If something is very different, you may have set the wrong heading, or misread the compass or the chart.
Time check at each waypoint. Write the actual time next to the planned time. If you are early or late, work out the real groundspeed and see if the wind is different from the forecast.
The fuel habit. At a fixed interval and at every waypoint, write down the time, the fuel gauge reading, the tank in use, and the fuel you expected to have left. Compare the calculation with the gauges. Fuel gauges can be inaccurate, so a calculation based on time and flow is your main check, and a difference between the two is a warning.
Revise the plan. With the real groundspeed you can calculate a new arrival time and the fuel you will land with. If it is less than the plan, decide now, not when the tanks are low.

5. Diverting, and the 1-in-60 rule

When to divert. A diversion is a normal tool, not a failure. Decide to divert early if the weather ahead is worse than you can fly in, if the fuel will not leave the final reserve at the destination, if you are not sure of your position for too long, or if you are tired or unwell. Set decision points before the flight, such as “if the cloud base is below X at point Y, I turn back”. A decision made on the ground is easier to follow than one made in the air under pressure.

The 1-in-60 rule. At a distance of 60 NM, an error of 1° puts you about 1 NM off track. This gives two formulas:

Track error (°) ≈ off-track distance × 60 ÷ distance flown Closing angle (°) ≈ off-track distance × 60 ÷ distance to go

To return to your track at the destination, turn by the sum of the two angles, towards the track. The rule is accurate for small angles, up to roughly 20°, and gets worse for larger ones.

Example (invented numbers). You find that you are 4 NM to the right of track, after 40 NM, with 20 NM to go.

Track error: 4 × 60 ÷ 40 = 6°. You have been drifting about 6° to the right of the track.
Closing angle: 4 × 60 ÷ 20 = 12°.
Total correction: 6 + 12 = 18° to the left. Alter your heading by 18° to the left, and you will arrive at the destination.

If you regain the track before the destination, take away the closing angle and keep the 6°, so you stop drifting. The same rule helps with a diversion to a new place: measure the distance, estimate the angle on the chart, and use the rule to pick a first heading before you have done the full calculation.

For real flights use the official charts, the weather and NOTAM briefing, the AIP of the country, and the flight manual of your aeroplane to plan, and do not rely on these invented numbers. If you are unsure of your position, say so early, and ask for help on the radio.

6. Try it yourself

Work each one out on paper first, then open the answer to compare. The numbers are invented.

All numbers invented. An aeroplane burns 30 litres per hour in the cruise. Leg 1 is 36 NM at a groundspeed of 90 kt. Leg 2 is 45 NM at a groundspeed of 90 kt. Fill in the time and the fuel for each leg and the totals for the trip.
Show the answer
Time (min) = distance ÷ groundspeed × 60.
Leg 1: 36 ÷ 90 × 60 = 24 min, and fuel = 24 ÷ 60 × 30 = 12 L. Leg 2: 45 ÷ 90 × 60 = 30 min, and fuel = 30 ÷ 60 × 30 = 15 L.
Trip: 81 NM, 54 min, 27 L.
Using the trip from the last exercise (27 L), add the other parts. These amounts are invented to show the method and are not what any regulation requires: taxi 3 L, contingency 10 per cent of the trip fuel, 15 minutes to an alternate at 30 L/h, final reserve 30 minutes at 30 L/h. The usable fuel in the tanks is 70 L. Is the flight possible, and how much is spare?
Show the answer
Contingency: 10 per cent of 27 = 2.7, rounded up to 3 L. Alternate: 15 ÷ 60 × 30 = 7.5, rounded up to 8 L. Final reserve: 30 ÷ 60 × 30 = 15 L.
Total = taxi 3 + trip 27 + contingency 3 + alternate 8 + final reserve 15 = 56 L. The tanks hold 70 L, so the flight is possible, with 14 L spare for extra margin.
You round fuel up, not down, and the 15 L final reserve must still be in the tank when you land. Never plan to use it. The real amounts come from the regulation, your school and the flight manual.
Invented numbers. After 30 NM you find that you are 3 NM to the left of your track, with 45 NM still to go. Use the 1-in-60 rule to find the track error, the closing angle and the heading change you need to arrive at the destination. In which direction do you turn?
Show the answer
Track error = off-track distance × 60 ÷ distance flown = 3 × 60 ÷ 30 = 6° (you have been drifting about 6° to the left of the track).
Closing angle = off-track distance × 60 ÷ distance to go = 3 × 60 ÷ 45 = 4°.
Total correction = 6 + 4 = 10° to the right, towards the track. If you regain the track before the destination, take away the closing angle and keep the 6° so that you stop drifting.

7. Watch

A walk-through of filling in a VFR navigation log. It is from an American instructor, so the form and some rules differ from Europe. The method is the same.

Open on YouTube if the player does not load. Not made by VectorEFB; check what you learn against your flying school’s material and your instructor.

More to watch

A second walk-through of a navigation log, leg by leg. This video is American, so the form, wording and some rules differ from European (ICAO/EASA) practice, but the method is the same.

Open on YouTube if the player does not load. Not made by VectorEFB.

8. Check yourself

Five original practice questions. Answer them, press Check answers and read each explanation.

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