What Does 'Mayday Fuel' Mean? Reserve Fuel, Explained

What the 2026 report describes

The UK Air Accidents Investigation Branch (AAIB) report published on 24 September 2026 describes a flight from Italy to Scotland on 3 October 2025, in a storm. Its fuel plan included taxi and trip fuel, 5 percent contingency, fuel to an alternate airport and 30 minutes of final reserve; the commander also loaded about 1,300 kg extra, roughly an hour and 12 minutes of flying. Our windshear page covers the three warnings that followed.

After two windshear escapes, the crew asked to divert to the airport they had chosen as their alternate. The request was refused; the report found that, under that airport's own policies, it should have been accepted, and that the refusal appeared to come from a breakdown in communication inside the airport. The crew diverted to a second airport instead, met a third windshear warning there, declared "mayday mayday mayday fuel" and flew on to their preferred alternate. They landed with 363 kg of fuel against a final reserve of 1,101 kg, 1 hour 45 minutes after the first go-around. No one was hurt.

The report notes that at go-around power the engines burned about 120 kg a minute, and that when a low fuel alert came on there was a chance to review the decision, because the second airport was closer. The airport has since restated that it accepts diversions whenever it has room. We report the findings; we do not judge the crew.

How fuel reserves work

The UK Civil Aviation Authority's safety notice on the subject sets out three steps. The pilot in command must keep checking that there is enough fuel to reach an airport where a safe landing can be made with the planned final reserve still in the tanks, and should ask controllers about delays when that margin is at risk.

The second step is "MINIMUM FUEL": the flight is committed to one airport and any change to its clearance could mean landing with less than the final reserve. The notice is clear that this is not an emergency and that controllers are not required to give priority. The third step is the fuel emergency: when the fuel expected on landing at the nearest suitable airport is less than the final reserve, the pilot must declare it, by broadcasting "MAYDAY MAYDAY MAYDAY FUEL".

US rules work the same way. A US domestic airline flight must carry enough fuel to reach its destination, then fly to the most distant alternate airport, then fly for 45 minutes at normal cruising consumption. The FAA's manual calls "minimum fuel" an advisory, not an emergency, and tells pilots to declare an emergency and report fuel remaining in minutes if they need priority.

Why holding and diversions are normal

Reserves exist so that a crew never has to choose between a dangerous approach and running out of fuel. A wait in a holding pattern or a diversion on a stormy day is that system working: the crew is spending some of its planned extra fuel and protecting the reserve. If you hear the word Mayday on a flight, it means the crew is asking for priority, and controllers will clear the way.

In AeroFox

AeroFox does not simulate fuel planning. In the free emergency lesson Hand It to the Autopilot, though, you make a distress call yourself: "Mayday" on 121.5 MHz, and the emergency code 7700. Our page on squawk 7700 explains what controllers see when that code appears.