The Point of No Return With 100 kg to Spare
Flight 214, a twin-jet, is 1 h 05 min from Calder (KCLD) at FL290 with 3 700 kg of fuel on board. The release carried taxi 200 kg, trip 7 900 kg, contingency 5 % (395 kg), destination alternate Stern (KSTN) 1 150 kg and final reserve 1 200 kg (30 min). The dispatcher added no extra fuel even though KCLD's TAF carried PROB30 TSRA for the arrival window. The flight has been held level at FL290 instead of the planned FL350 for 40 minutes because of traffic, and the headwind is 12 kt stronger than forecast. The FMS now predicts 2 600 kg to KCLD. KSTN is 130 nm ahead, 10 nm left of track, CAVOK; flight planning gives 1 150 kg from the present position to touchdown there, including the approach. KCLD's TAF has just been amended to TEMPO 1 500 ft broken, 4 km, TSRA.
1. Calculate the fuel that would remain on landing at KCLD and at KSTN. Is the flight currently in a MINIMUM FUEL or a MAYDAY FUEL situation?
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At KCLD: 3 700 − 2 600 = 1 100 kg, against a planned final reserve of 1 200 kg - 100 kg (about 2.5 min) short, and that assumes a straight-in landing. The TAF now offers TSRA; a go-around and second approach costs roughly 200–300 kg, which would leave about 850 kg.
At KSTN: 3 700 − 1 150 = 2 550 kg, i.e. 1 350 kg above the final reserve.
Classification:
- MINIMUM FUEL - committed to land at a specific aerodrome and any change to the clearance may result in landing below the final reserve.
- MAYDAY FUEL - the calculated fuel on landing at the nearest aerodrome where a safe landing can be made is below the final reserve.
At this instant the nearest aerodrome where a safe landing can be made is KSTN, and the calculation there gives 2 550 kg. The flight is therefore not yet in either state. The moment it passes KSTN and commits to KCLD the calculation reads 1 100 kg < 1 200 kg, which is MAYDAY FUEL, not merely MINIMUM FUEL - the projected landing fuel is already below the reserve, not merely at risk of it.
The whole case turns on that: the state changes from 'no declaration required' to 'emergency' at a geographic point, and that point is now.
2. What do you tell the crew, what do you do in the next ten minutes, and what must you refuse?
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To the crew: divert to KSTN now, with the numbers spelled out so both of you are working from the same figure (2 550 kg landing at KSTN versus 1 100 kg at KCLD). The declaration itself is the commander's; if the crew elects to continue toward KCLD, they must declare MINIMUM FUEL on the radio and the situation becomes MAYDAY FUEL as soon as the commitment is made.
Dispatcher actions:
- Confirm KSTN is suitable, not just open - runway length and PCN against the landing weight, RFF category, no closing NOTAM, customs/handling for the passengers.
- Pass the diversion to operations, load control and the destination station; cancel the KCLD handling.
- Ask ATC for the most direct routing and, if the crew declares, for priority.
- Record the time, the figures used, the decision and who made it; raise an occurrence report - a fuel emergency/degradation of the reserves is normally reportable.
Refuse: any hold, any speed reduction, any vectors off track, and above all the 'one approach at KCLD and then divert' plan. From KCLD, KSTN is roughly 30 minutes away (about 1 150 kg); the fuel left after landing at KCLD would not cover it. The go-around is not available as a fallback, which is exactly why the TAF matters more than the 100 kg arithmetic.
3. Where did this plan go wrong, and what planning technique would have prevented it?
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What consumed the margin:
- Contingency was 395 kg - about 10 minutes. The level-off at FL290 burns roughly 250 kg/h more than FL350; over 1.5 hours that alone is around 375 kg.
- A 12 kt stronger headwind over the remaining 1.5 hours adds roughly 120–140 kg.
- Together they exceed the entire contingency. The PROB30 TSRA was the cue to carry extra fuel for a probable missed approach (typically 15 min, about 600 kg); none was carried.
The fix is a decision point, not a bigger number: compute, before departure, the last position from which the en-route alternate can be reached and still land with final reserve plus a working margin. That position is usually well before the destination alternate becomes relevant, because it is measured from the aircraft's present position, not from the destination. Put it on the flight plan as a time and a fuel figure, and give the crew a trigger: 'passing this point with less than X, you divert'.
Also validate contingency against the actual forecast wind and any likely ATC level restriction, and treat a destination PROB30 of convective weather as a trigger for extra fuel rather than as noise.