Flight fuel reserve calculator

Invalid or missing numbers fail with invalid_input and are not billed.

What trip, alternate, reserve, and contingency fuel mean

Trip fuel is the fuel required to fly from departure to destination at the planned burn rate: burn_rate multiplied by flight time converted to hours. Final reserve fuel is a time-based holding quantity that must still be in the tanks on arrival at the destination or the alternate; regulations typically quote it in minutes, so this calculator takes reserve_minutes and converts it to hours before multiplying by burn rate. Contingency fuel, when you supply contingency_percent, is a fraction of trip fuel that covers wind errors, routing changes, and level changes; five percent is a common planning figure, and zero percent is accepted when you want a raw trip-plus-alternate-plus-reserve total.

Input contract, units, and response fields

Values are rounded to twelve decimal places for stable goldens. POST a JSON body with three required finite numbers: burn_rate, the hourly fuel consumption in any consistent unit such as gallons per hour, litres per hour, or kilograms per hour; flight_time, the planned trip duration; and reserve_minutes, the required final reserve expressed in minutes. Optional flight_time_unit is hours by default or minutes when the trip is entered that way. Optional alternate_time is the time from destination to the alternate, defaulting to zero when you are planning a flight without an alternate; alternate_time_unit is hours by default or minutes. Optional contingency_percent is a number from zero to one hundred inclusive, defaulting to zero. Each numeric field may arrive as a JSON number or as a numeric string; missing fields, empty strings, non-finite values, negative times, a non-positive burn_rate, and a contingency outside zero to one hundred fail with invalid_input naming the field and are not billed. On success the body echoes the cleaned inputs and the normalised times in hours, then reports trip_fuel, alternate_fuel, reserve_fuel, contingency_fuel, and total_fuel in the same physical unit as burn_rate. endurance_hours and endurance_minutes restate how long that total will last at the given burn. result duplicates total_fuel for clients that always read a single numeric field. A formula string restates the four-term identity, method is trip_plus_alternate_plus_reserve_plus_contingency, and message summarises the stack in plain language. Example: burn_rate twelve, flight_time two point five hours, reserve_minutes forty-five, alternate_time zero point five hours, and contingency_percent five yields trip fuel thirty, alternate six, reserve nine, contingency one point five, and total forty-six point five.

Where a flight fuel reserve API earns its keep

General-aviation pilots and instructors use a flight fuel reserve calculator before VFR and IFR cross-countries so the legal reserve and a realistic alternate are not forgotten when someone multiplies gallons per hour by estimated time en route on a napkin. Charter and airline dispatch desks need the same four-term stack for a single sector without opening a full flight-planning suite: they already hold burn, trip time, alternate time, and company reserve minutes. Training organisations and ATPL exam generators need a deterministic oracle that treats reserve as minutes, accepts trip time in hours or minutes, and never silently drops contingency. Engineering notebooks that already store fuel flow and estimated times can call a tiny parse API instead of re-deriving the same arithmetic in every language binding. Keep requests small, pin total_fuel and the four-term breakdown in tests, and you get reproducible planning fuel for briefings, LMS plugins, and edge workers without standing up a performance-engineering library of your own. This endpoint does not compute weight and balance, takeoff performance, or great-circle time; it only converts the fuel policy you already chose into a total you can load.