Guide for student pilots
How much fuel for a VFR flight: planning and reserves
Running out of fuel is entirely preventable, and the sums are simple. This guide shows how to build a fuel figure from its parts, how to check it against the tanks and the weight limit, and how to watch it in the air. Your school’s rules and the aeroplane’s flight manual come first.
Written for training. Rules and figures differ between countries and operators, so check them against your own regulations, your school’s manual and your instructor.
1. The parts of a fuel plan
A fuel figure is a sum of separate parts, each with its own reason. Add them up, then check that the total fits in the usable fuel in the tanks.
- Taxi. From engine start to the start of the take-off roll, including the run-up. Use the figure in your flight manual or your school’s usual number.
- Trip. From take-off to landing at the destination: climb, cruise and descent, using the forecast wind at your planned level. Climb burns more fuel than cruise, so a cruise-only figure is a little low.
- Contingency. A margin for what never goes exactly to plan: a stronger headwind, a detour, a longer wait. Many schools use a percentage of the trip fuel, commonly 5 to 10 per cent, often with a minimum. Use your school’s rule.
- Alternate. The fuel to fly from the destination to an alternate aerodrome, if you need one because the weather or the aerodrome may stop you landing. Work it out on the route you would really fly, with the wind at that level.
- Final reserve. The fuel that must still be in the tanks when you land. It is not part of the plan you spend. It is the last margin when everything else has gone wrong.
- Additional. Anything extra you decide to carry, for example for a forecast delay or an unfamiliar airfield. More fuel is more mass, so check the weight and balance.
In Europe, private flights in aeroplanes fall under EASA Part-NCO. NCO.OP.125 requires enough fuel for the planned flight plus a reserve, and its acceptable means of compliance give a final reserve of 30 minutes at holding speed at 1,500 ft above the destination for a day VFR flight and 45 minutes at night. National rules and school rules can be stricter, and many schools plan 45 minutes by day. Check the current text and use your school’s figure.
2. A worked example
All the numbers are invented to show the method. The aeroplane burns 30 litres per hour in the cruise and has 100 litres of usable fuel. The route is 120 NM at a true airspeed of 100 kt, with a 15 kt headwind, so the groundspeed is about 85 kt. The alternate is 15 minutes away.
| Part | How it is worked out | Fuel |
|---|---|---|
| Taxi | From the flight manual | 3 L |
| Trip | 120 ÷ 85 = 1.41 h = 85 min; 85 ÷ 60 × 30 = 42.5, rounded up | 43 L |
| Contingency | 10 per cent of 43 = 4.3, rounded up | 5 L |
| Alternate | 15 ÷ 60 × 30 = 7.5, rounded up | 8 L |
| Final reserve | 30 ÷ 60 × 30 | 15 L |
| Total | 74 L |
The tanks hold 100 litres of usable fuel, so the flight is possible with 26 litres spare. Two checks follow from the table.
- The wind cost fuel. In still air the trip would take 72 minutes and 36 litres. The headwind added about 6 litres. Plan with the forecast wind at your level, not with still air.
- The landing check. On arrival over the destination you should still have at least the alternate plus the final reserve: 8 + 15 = 23 litres. If your running calculation says you will have less, you have a decision to make now, not later (section 5).
Always round fuel up, never down. The time and fuel calculator in the Learning hub does the leg sums, and the lesson on fuel, the navigation log and monitoring in flight works through a full example.
3. Check the number against the aeroplane
- Usable, not total. The tanks hold some fuel you cannot use. Plan against the usable figure in the flight manual.
- Dip or look, do not trust the gauge. Fuel gauges are indications. Check the quantity by looking in the tanks or using the dipstick, and compare it with what you planned. Drain a sample for water and the right colour and smell, as you were taught.
- Fuel is weight. Avgas 100LL weighs about 0.72 kg per litre (6 lb per US gallon), so 74 litres is about 53 kg. Fill the tanks and the aeroplane may be over its maximum take-off mass or out of its balance limits with the people and baggage on board. Work the loading sheet with the real fuel, and see loading and the centre of gravity.
- One unit all the way through. Litres and US gallons (1 US gallon is 3.785 litres) both appear in flight manuals, fuel pumps and fuel orders. Pick one for the whole calculation. The unit converter helps you check.
4. What makes the real number bigger
- A headwind stronger than forecast, or a different wind at your level. Check the wind for the level you will really fly.
- A long taxi, a long hold at the runway, or a delayed departure with the engine running.
- A climb to a higher level, a hot day or a high airfield: the climb takes longer and burns more. See density altitude.
- A mixture or power setting richer or higher than the one in your plan.
- A detour around weather or airspace, and a go-around or a longer circuit at the other end.
5. Fuel in the air
The plan is a prediction, so compare it with what is happening. At every checkpoint, and at a fixed interval such as every 15 minutes, write down the time, the fuel the plan says you should have, and the gauge reading. Your calculation from time and fuel flow is the main check, and a gap between it and the gauges is a warning.
- Predict the landing fuel. With the groundspeed you are really making, work out when you will arrive and how much fuel you will have then.
- Decide early. If the prediction for the destination is less than the alternate plus the final reserve, or you will land with less than the final reserve, divert or land sooner, while you still have choices. Never plan to use the final reserve.
- Say so. If you expect to land with less than your final reserve, tell ATC early and say what you need. Your instructor will teach you the exact phraseology, and the lesson on Mayday, Pan Pan and lost communications covers urgency and distress calls.
6. Common mistakes
- Planning with still-air numbers, or with the surface wind instead of the wind at your level.
- Counting the final reserve as fuel you can use.
- Mixing litres and US gallons, or using total instead of usable fuel.
- Using the day reserve for a flight that may end after dark.
- Ordering fuel at an unfamiliar airfield in the wrong unit, or without checking the grade. Say the unit and the grade aloud and check the total on the pump.
- Trusting the gauges and stopping the running calculation.
Where VectorEFB can help
In the Route panel you enter the fuel on board, the burn per hour, the taxi fuel and your reserve in minutes, in litres or US gallons. The nav log then shows the fuel used and the fuel remaining at the end of each leg, and a notice appears if the landing fuel falls below your reserve. The nav log counts cruise burn only, so add your own climb and alternate figures. The Tools panel has a fuel calculator that adds contingency, alternate and extra fuel. Use them to check your own sums.
VectorEFB is a training and situational awareness aid. It is not certified for navigation. Do the planning yourself first, and use official charts, the AIP, NOTAMs and a proper weather briefing for real flights.
Flying as a licensed pilot? The pilot page shows the same tools.
Next: wind correction angle and groundspeed. All guides are listed on the guides page.