What Is Fuel Reserve? Definition & Meaning in Aviation
A fuel reserve is the extra fuel an aircraft must carry beyond the amount needed to reach its destination, to cover delays, diversions and contingencies.
In plain language
Regulations set minimums, including a final reserve, often enough for about 30 minutes of flight at holding speed for jets. Crews declare an emergency if they might land below it.
Example
An aircraft held for traffic is using its reserve fuel margin, which is one reason crews may divert instead of holding for a long time.
Why it matters
Reserve fuel is why aircraft do not simply wait indefinitely when an airport is closed. When reserves run low, crews divert, which can explain sudden changes in plans.