Protect the fuel decision margin

Why is predicted landing fuel more useful than a tank percentage?

Calculate predicted landing fuel and its margin above a supplied reserve, accounting for changes in route and consumption.

Understand the mechanism

Usable fuel remaining describes the present supply. An operational decision also needs the fuel required to reach a place where a safe landing can be made under the expected conditions. Route, wind, altitude, aircraft state and delays change that requirement. Comparing actual fuel with the operational flight plan identifies a trend; investigating the cause matters more than simply writing a smaller number beside the waypoint.

The current fuel/energy scheme distinguishes planned components. Extra fuel addresses anticipated delay or specific operational constraints, while discretionary fuel is added when required by the commander. The ECQB 2026 update describes the basic scheme, the 3% reduced-contingency variation and isolated-aerodrome variation as accommodated by the current objectives. It does not make every individual scheme an examination requirement. Numerical percentages must remain tied to their applicable scheme and conditions.

Apply the evidence

A simple projection is landing fuel=current usable fuel−estimated burn to landing. This arithmetic exposes a margin but omits changes in conditions unless the estimated burn is updated. Final reserve is protected fuel for the applicable emergency-planning purpose; it is not a routine holding allowance. A decision made before the final reserve is threatened can preserve choices that disappear if the crew wait for the tank quantity itself to look small.

Worked case · synthetic training operation

The synthetic aircraft has 4,800 kg usable fuel. Updated burn to a suitable landing is 3,100 kg and the supplied final reserve is 1,200 kg. Predicted landing fuel is 1,700 kg, giving 500 kg above that reserve. A further 600 kg delay would reduce the estimate to 1,100 kg. The early comparison identifies that the proposed delay consumes more than the available margin. All figures are fictional; the method requires a current burn estimate and a genuinely suitable landing option.

When does a fuel concern become a minimum-fuel or emergency message?

Distinguish minimum-fuel and fuel-emergency communication using the landing commitment, predicted fuel and planned final reserve.

Understand the mechanism

For aeroplanes, minimum fuel communication applies when the commander has committed to land at a specific aerodrome and calculates that any change to the existing clearance may result in landing with less than planned final reserve. It warns ATC about the absence of additional delay margin. It is not an emergency declaration and does not by itself request emergency priority. The actual condition, rather than an arbitrary tank percentage, governs the message.

A fuel emergency is declared with the prescribed MAYDAY FUEL transmission when estimated usable fuel on landing at the nearest aerodrome where a safe landing can be made is less than planned final reserve. The comparison concerns estimated landing fuel, not waiting until fuel on board has already fallen below the reserve figure. A safe landing location must satisfy the relevant conditions; the geographically closest runway is not necessarily suitable.

Apply the evidence

The communication belongs within continued fuel monitoring and decisive replanning. Receiving a shorter vector does not erase the need to recompute the estimate. If conditions worsen, a previous minimum-fuel message may no longer describe the situation. Conversely, a crew can act early to avoid approaching either threshold. The lab supplies a fictional reserve and predicted landing estimate; it illustrates the logical distinction without selecting an aircraft’s reserve or diversion procedure.

Worked case · synthetic training operation

In the synthetic case, the aircraft is committed to aerodromeA. Its projected landing fuel is 1,250 kg against a planned final reserve of 1,200 kg, and any clearance extension would consume more than 50 kg. That fits the stated minimum-fuel condition. Later the nearest safe landing option is estimated at 1,100 kg: it is now below final reserve, supporting the emergency declaration. The distinction is 50 kg above versus 100 kg below at landing under the stated facts, not whether a warning light has illuminated.

Can you explain and apply the mechanism?

Four original questions. Work from the stated facts, then compare your reasoning with the explanation.