IFR Alternate Fuel Reserve Planner

Introduction: planning IFR alternate, holding, and reserve fuel

IFR fuel planning must account for more than the direct route to the filed destination. A usable plan considers the destination leg, a possible continuation to an alternate, time that may be spent holding, and the reserve policy that applies to the operation. Forecast winds, vectors, a missed approach, and route changes can all change the time aloft and therefore the gallons required. Carrying too little fuel can leave no practical options; carrying more also has weight, balance, payload, and cost consequences. This IFR Alternate Fuel Reserve Planner organizes those fuel allowances into one predeparture estimate.

The planner separates the gallons for the primary leg, alternate leg, planned holding, reserve time, climb and maneuvering, taxi and run-up, and an extra contingency. It then compares the total with the fuel on board entered for departure. If the margin is narrow, test a different alternate, revised groundspeed, or a fuel stop before committing to the flight. The results table applies the same 15% groundspeed change to both en-route legs, making it easier to see how a broad wind forecast error affects the required fuel.

A written IFR fuel calculation is useful when reviewing a flight with a dispatcher, instructor, passenger, or another pilot. After calculating, the page can download the displayed planning scenarios as a CSV file. That record is only as reliable as the route, weather, aircraft performance, and usable-fuel assumptions entered into it, so update those assumptions when conditions change rather than treating an earlier estimate as a dispatch release.

Formulas underpinning IFR alternate and reserve fuel

This IFR fuel planner converts each distance into hours using its planned groundspeed, multiplies those hours by cruise fuel burn, and then adds the entered fixed allowances. The calculator uses the following relationship.

For this IFR alternate calculation, F is total departure fuel required in gallons, B is cruise burn in gallons per hour, D is primary-leg distance, and V is primary-leg groundspeed. V_a is the alternate-leg groundspeed, while H and R are holding and reserve minutes. C, T, and E are the climb/maneuver, taxi/run-up, and contingency gallons. The displayed fuel weight is calculated separately by multiplying the fuel-on-board entry—not the required-fuel total—by the selected pounds-per-gallon density.

The IFR planner also reports an endurance estimate after the entered taxi allowance: it subtracts taxi gallons from fuel on board and divides the remainder by cruise burn. Its “available beyond the regulatory reserve” figure subtracts only the reserve minutes entered from that endurance estimate. It does not subtract the destination, alternate, holding, climb, or contingency portions from that particular display, so use the required-fuel total and margin as the primary go/no-go comparison. The estimated cost is the required gallons multiplied by the entered price per gallon.

Worked example: an IFR destination, alternate, holding, and reserve plan

Consider the calculator’s default planning case: a 320-nautical-mile primary leg at 135 knots with a cruise burn of 10.5 gallons per hour. The alternate is 60 nautical miles beyond the destination at 125 knots. The entered allowances are 3 gallons for climb and maneuvering, 20 minutes of holding, a 45-minute reserve, 1.5 gallons for taxi and run-up, and 2 contingency gallons. Fuel on board is 56 gallons, fuel density is 6 pounds per gallon, and the estimated price is $5.75 per gallon.

For this IFR scenario, the primary leg takes about 2.37 hours and uses about 24.9 gallons. The alternate leg takes 0.48 hours and uses about 5.0 gallons. Holding uses 3.5 gallons and the 45-minute reserve uses about 7.9 gallons. Adding the 6.5 gallons of climb, taxi, and contingency allowances produces a required departure fuel of 47.8 gallons. Against 56 gallons on board, the displayed margin is 8.2 gallons. The planner also reports approximately 336 pounds for the full 56-gallon load and an estimated required-fuel cost of about $275.

The 15% groundspeed cases change both the primary and alternate groundspeeds. At 85% of the forecast speeds, the primary leg is about 2.79 hours and the total requirement is about 53.1 gallons, leaving roughly 2.9 gallons of margin. At 115% of forecast speeds, the requirement falls to about 43.9 gallons, leaving about 12.1 gallons. These are planning comparisons, not promises about actual winds: reassess the remaining fuel, current burn, weather, and diversion options throughout the flight.

Comparison table: IFR groundspeed sensitivity and fuel margin

The IFR groundspeed sensitivity table below illustrates the same three scenarios that the calculator generates after submission. Because a speed multiplier is applied to the destination and alternate legs, slower groundspeeds increase fuel for both route segments; holding, reserve, climb, taxi, and contingency entries remain unchanged.

For IFR alternate fuel planning, the table is most useful for identifying how little margin remains when progress is slower than forecast. The cost column is the estimated value of the required fuel at the entered price; it is not a quote for fuel actually purchased. Save the CSV only as a scenario record, and revise it if the alternate, route, winds, fuel burn, or fuel-on-board figure changes.

Limitations, assumptions, and IFR fuel-planning practices

This IFR fuel planner assumes one cruise burn rate for the destination leg, alternate leg, planned holding, and reserve. Actual burn can differ with power setting, altitude, mixture, temperature, aircraft configuration, and a holding speed chosen for endurance. If holding or alternate operations use a materially different burn than cruise, use a suitably conservative burn entry or include additional contingency fuel. The alternate groundspeed is likewise a planning value; winds and routing may differ by altitude and direction.

Taxi and run-up consumption can vary substantially with airport layout, delays, warm-up, and ground operations. Use aircraft records to set that allowance, and account separately for unusable fuel, tank limitations, and weight-and-balance constraints in accordance with the aircraft documentation. The reserve field accepts the minutes you enter; it does not determine which reserve rule or alternate requirement applies to a particular jurisdiction or operation. This calculator is a planning aid, and the pilot in command remains responsible for current requirements, aircraft limitations, weather information, and safe fuel decisions.

How to use this IFR alternate fuel reserve planner

1. Enter Distance to destination (nautical miles) for the planned primary IFR leg.
2. Enter Planned average ground speed (knots) for that primary leg.
3. Enter Cruise fuel burn (gallons per hour) from the performance assumptions you are using for the flight.
4. Submit the IFR fuel plan, then test a revised wind, alternate, or contingency assumption before relying on the fuel margin.