Holding for Weather with 2,700 kg On Board
Your twin-engine jet is cruising at FL350, 50 minutes from destination, with 2,700 kg of fuel on board. Anti-ice is on and the actual fuel flow is 1,350 kg/h. The operational flight plan showed trip fuel 6,400 kg, contingency 320 kg, alternate fuel 850 kg, final reserve 650 kg (30 minutes at 1,300 kg/h) and taxi 200 kg. Destination weather has deteriorated: RVR 400 m against CAT I minima of 550 m, and the trend is worsening. The alternate is 25 minutes away with weather well above minima; a diversion and approach there requires 662 kg including the missed approach. ATC offers a 20-minute hold at destination for weather improvement and says it is the only delay, expecting RVR to improve to 700 m. Your co-pilot suggests holding and then diverting if it does not improve.
1. Using the figures given, calculate the maximum hold time at destination that still leaves the diversion to the alternate and the final reserve intact. Does the 20-minute hold fit?
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Fuel to destination: 50 min x 1,350 kg/h / 60 = 1,125 kg. Fuel needed after reaching destination to divert: 662 kg (diversion, approach and missed approach). Protected final reserve: 650 kg. Total needed from the present position to divert at destination: 1,125 + 662 + 650 = 2,437 kg. Fuel on board: 2,700 kg, so the surplus is 263 kg. Maximum hold: 263 / 1,350 x 60 = 11.7 min, so about 11 minutes. A 20-minute hold burns 20/60 x 1,350 = 450 kg and leaves 2,250 kg at the end of the hold. Reaching destination then leaves 1,125 kg; diverting would leave 1,125 - 662 = 463 kg, which is 187 kg below the 650 kg final reserve. The 20-minute hold does not fit. Two further points matter. The contingency fuel is already part of the 2,700 kg and may be used, but the final reserve is not available for planning. Also, at the actual flow of 1,350 kg/h the 650 kg reserve is only about 28.9 minutes, not 30 minutes, so the real endurance margin is slightly worse than the flight plan suggests.
2. If you nevertheless accept the hold, what fuel declarations are required, when, and with what phraseology?
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MINIMUM FUEL is declared when the aircraft is committed to landing at a specific aerodrome and any change to the established plan would result in landing below the planned final reserve. After accepting a 20-minute hold that is exactly the situation: diverting would leave 463 kg, below 650 kg. The declaration is therefore required as soon as the hold is accepted, not when the fuel gauge approaches the reserve. MAYDAY MAYDAY MAYDAY FUEL is declared when the calculated fuel on landing at the nearest suitable aerodrome would be below the final reserve. If a further delay, a missed approach or a change of runway means the expected landing fuel falls below 650 kg, the distress call is required. Phraseology: 'MINIMUM FUEL' or 'MAYDAY MAYDAY MAYDAY FUEL', with position, intentions and assistance required. A MINIMUM FUEL call does not by itself give priority; a MAYDAY FUEL does. Do not wait for a low-fuel warning to make either call. Also advise the operator and the cabin crew early, because the cabin needs time to prepare for a diversion and a possible long wait on the ground.
3. Decide and justify. What do you tell ATC and the cabin?
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Decision: do not accept the 20-minute hold. The destination is already below CAT I minima (RVR 400 m against 550 m) and the trend is worsening, so there is no realistic expectation of an approach at the end of the hold. The 'expected 700 m' is a forecast, not a report, and the approach ban would prevent continuing past the final approach fix if the RVR were still below 550 m. Holding consumes the only fuel that keeps the alternate and the final reserve intact. The safer option is to divert now, while 2,700 - 662 = 2,038 kg remains, which is 1,388 kg above the final reserve. If there were a realistic chance of improvement, the maximum useful hold would be about 11 minutes, with a running fuel check every 5 minutes and a pre-briefed diversion trigger. That is not the situation here. To ATC: 'Unable to hold due fuel, request diversion to ...' If a hold were accepted, the correct call would be MINIMUM FUEL, followed by MAYDAY FUEL if the landing fuel fell below the reserve. Do not accept a clearance that commits you to a destination you cannot reach with the reserve. To the cabin: a short, factual announcement of the diversion and the new arrival time, with no speculation. To the operator: advise the diversion and the fuel state. Commercial pressure and 180 passengers do not override the reserve.