Fuel Decision After an ATC Reroute
You are planning a twin-jet sector with the following fuel figures: taxi 120 kg, trip fuel 2,150 kg, contingency 5% of trip fuel, alternate fuel 540 kg, final reserve 30 min at 750 kg/h, and extra fuel 150 kg. The destination forecast requires an alternate. While 180 NM before destination, ATC advises that a military zone is active and the reroute will add 20 min at an average fuel flow of 800 kg/h. The crew has already burned the taxi fuel and is on the planned trip fuel profile. The destination weather is at the approach limit, and the alternate is 70 NM away. You must decide whether to continue to destination, divert now, or request a shortcut.
1. Calculate the planned total fuel, the fuel remaining at destination after the reroute, and whether the alternate plus final reserve can still be protected.
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Planned fuel:
| Item | kg |
|---|---|
| Taxi | 120 |
| Trip | 2,150 |
| Contingency 5% | 107.5 |
| Alternate | 540 |
| Final reserve (30 min at 750 kg/h) | 375 |
| Extra | 150 |
| Total | 3,442.5 |
Reroute burn = 20 min × 800 kg/h = 266.7 kg.
Fuel at destination = 3,442.5 − 120 − 2,150 − 266.7 = 905.8 kg.
Required for alternate + final reserve = 540 + 375 = 915 kg. The aircraft is about 9 kg short. Final reserve alone is still intact by 530.8 kg, but the planned alternate fuel is not fully protected. Continuing is only acceptable if landing at destination is assured; otherwise divert now or obtain a shortcut that restores the margin.
2. ATC offers a 10-minute shortcut instead of the reroute. Recalculate and state whether to accept it.
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Shortcut burn = 10 min × 800 kg/h = 133.3 kg.
Fuel at destination = 3,442.5 − 120 − 2,150 − 133.3 = 1,039.2 kg.
Margin over alternate + final reserve = 1,039.2 − 915 = 124.2 kg. This is a clear improvement over the 9 kg shortfall and restores a small but usable margin. Accept the shortcut, but continue to monitor fuel. If further delays occur, the crew should be prepared to declare minimum fuel and divert rather than arrive with the alternate fuel eroded.
3. What operational actions would you take if the shortcut is not available and the destination weather remains at the limit?
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With 905.8 kg at destination, the aircraft can land with final reserve intact, but it cannot then fly the 540 kg alternate and still keep 375 kg. Because the destination weather is at the approach limit, a go-around or diversion is credible. The prudent action is to divert now to the alternate while the fuel is available, or to request priority and a direct routing to destination only if landing is assured. Declare minimum fuel if ATC delay continues. Do not plan to arrive at destination and then divert; the fuel plan no longer protects that option.