Hola Jones -
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Let me give you an example of fuel savings (or available increased payload) with re-dispatch -
According to FAR 121, for a 747-200.
Example, flight from London to New York, with re-dispatch near Gander.
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LHR to JFK - airways distance 3,300 NM, assuming 50 kts headwind.
Trip fuel 75,400 Kg - Time 7:32
Reserve 10% of 7:32 or 46 minutes - 14,000 Kg
Missed approach - 2,000 kg
Fuel to alternate EWR - 4,000 kg
Holding 30 minutes above EWR - 9,000 kg
Fuel required LHR to JFK =
104,400 kg xxx
LHR to YQX (re-dispatch point at 50º West) distance 2,300 NM, 50 kts headwind.
Trip fuel 55,000 kg...
YQX to JFK - airways distance 1,100 NM, again 50 kts headwind.
Trip fuel 23,600 kg - Time 2:32
Reserve 10% of 2:32 or 16 minutes - 3,500 kg
Missed approach - 2,000 kg
Fuel to alternate EWR - 4,000 kg
Holding 30 minutes above EWR - 9,000 kg
Fuel required LHR to JFK with YQX re-dispatch =
97,100 kg xxx
Fuel savings shown here - 7,300 kg... nearly 10,000 liters...
You must have 42,100 kg remaining in the tanks to continue beyond YQX.
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You could also red-dispatch more than once if somewhat low on fuel.
I had situation where I got re-dispatched from YQX to BGR (Bangor, Maine) then JFK.
Drain the tanks of a few drops for my Zippo lighter please...
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Happy contrails