Fuel Planning for Pilots — Reserves, Climb Fuel, and the Numbers That Actually Matter

Running out of fuel is one of the most preventable ways to wreck an airplane, and it still happens every year. It almost never comes down to bad arithmetic. It comes from planning numbers that were optimistic from the start: a cruise burn from the POH at a power setting nobody actually flies, a climb that was never counted, a forecast headwind that turned out stronger, or a fuel gauge that was trusted more than it deserved. This guide covers the legal minimums, a planning method that builds in the things that usually get missed, and two worked examples.

The Legal Minimums

For airplanes, the reserve rules are in 14 CFR Part 91:

• VFR by day (91.151): enough fuel to fly to the first point of intended landing and, assuming normal cruising speed, to fly after that for at least 30 minutes.
• VFR at night (91.151): the same, but at least 45 minutes after reaching the first point of intended landing.
• IFR (91.167): enough fuel to fly to the destination, then to the alternate if one is required, and then for 45 minutes at normal cruising speed.

Notice the wording: the reserve is measured at normal cruising speed. That is why the CockpitCalc fuel calculator converts reserve minutes into fuel using your cruise burn rate. Notice also that these are minimums for planning. Landing with exactly 30 minutes in the tanks is legal, but most flight schools and many experienced pilots plan to land with an hour.

The Planning Formula

Each piece deserves its own number:

• Start, taxi, and takeoff. Many POHs publish an allowance for this — on the order of a gallon or so in a typical four-seat trainer. Use the figure from your book.
• Climb. A piston single climbing at full power burns far more than it does in cruise. POHs include a "time, fuel, and distance to climb" chart; use it. If you skip the chart, at least add a few extra minutes of cruise burn for each climb.
• Cruise. Use the burn rate for the power setting you will actually fly, at the altitude you will actually fly it, leaned the way you actually lean. If you have a fuel flow gauge, your own logged numbers are better than the book.
• Alternate (IFR). Fuel from the missed approach at the destination to the alternate, at cruise burn.
• Reserve. 30 or 45 minutes at cruise burn — or more, by personal minimum.

Worked Example: Night VFR Cross-Country

A four-seat trainer with a planning cruise burn of 9.0 gal/hr is planning a 2-hour flight (including the climb) that will end after dark. The POH start/taxi/takeoff allowance is 1.4 gallons.

• Trip fuel: 9.0 × 2.0 = 18.0 gal
• Night VFR reserve: 9.0 × 45 ÷ 60 = 6.75 gal
• Start/taxi/takeoff: 1.4 gal
• Total required: 18.0 + 6.75 + 1.4 = 26.15 gal, or about 157 lb at 6 lb/gal

If the airplane holds 53 gallons usable, that leaves plenty of margin — but the arithmetic is only as good as the 2-hour estimate. A 15-knot headwind on a 120-knot airplane stretches a 2-hour leg to about 2 hours 17 minutes, which costs roughly another 2.6 gallons. Run the numbers again with the forecast winds aloft, not the no-wind time.

Worked Example: IFR With an Alternate

An airplane burning 10 gal/hr plans a 1.5-hour flight to a destination that requires an alternate 30 minutes away. Taxi and runup allowance is 1.5 gallons.

• Destination: 10 × 1.5 = 15.0 gal
• Alternate: 10 × 0.5 = 5.0 gal
• Reserve: 10 × 45 ÷ 60 = 7.5 gal
• Taxi: 1.5 gal
• Total: 29.0 gal (174 lb)

Holding, vectors, and a missed approach are not included in the regulation's formula, but they happen. If the destination weather is near minimums, adding 15–30 minutes of extra fuel is cheap insurance.

Usable Fuel, Gauges, and Visual Checks

Every tank has some unusable fuel that the engine can't get to in all flight attitudes. Plan against usable fuel, which the POH lists separately from total capacity. The difference can be several gallons.

Light-aircraft fuel gauges are not precision instruments. Certification standards focus on the gauge reading correctly at empty in level flight, not on accuracy at every point in between. Before every flight, confirm the quantity visually or with a calibrated fuel dipstick, and in flight, keep time on each tank and compare actual burn to your plan.

Converting Fuel to Weight

Fuel is often the one load you can change at the last minute, so fuel planning and weight and balance belong together. If a full-fuel, four-adult load puts you over gross weight, the answer is a fuel stop, not a lighter assumption.

Using the CockpitCalc Fuel Calculator

1. Enter your planning burn rate in gal/hr (or L/hr after switching units).
2. Enter flight time including the climb, based on forecast winds.
3. Set the reserve in minutes — 30 for day VFR, 45 for night VFR or IFR, or your personal minimum.
4. For IFR, enter the alternate time; for VFR, leave it at zero.
5. Enter your taxi/contingency allowance, then calculate. Compare the total to usable fuel on board.