How to calculate and check if a/c can carry additional reserve fuel without affecting payload and if so how much?

Find payload and state if a/c can carry additional reserve fuel without affecting payload and if so how much?

• Max take off weight= 45000 lbs.
• Max landing weight= 40000 lbs.
• Flight fuel= 4000 lbs.
• Reserve fuel= 800 lbs.
• Empty weight= 25000 lbs.

So, By calculating the take off weight using the above figures:

• TOW = Landing weight + Flight Fuel = 44000lbs

• Payload = TOW - (Empty Weight + Total Fuel)

• Payload = 44000lbs - (25000 + 4000 + 800)

Now how should I calculate and check if a/c can carry additional reserve fuel without affecting payload and if so how much?

• LW1 = 25,000 (EW) + 800 (reserve) = 25,800 lbs

The maximum allowed payload, as regards to LW, is:

• Payload = 40,000 (MLW) - 25,800 (LW1) = 14,200 lbs

With this payload and the trip fuel, the TOW is:

• TOW = 25,000 (EW) + 800 (reserve) + 14,200 (payload) + 4,000 (trip) = 44,000 lbs

This TOW is 1,000 lbs lower than MTOW, so you can takeoff.

With this payload the new LW is:

• LW2 = 25,000 (EW) + 800 (reserve) + 14,200 (payload) = 40,000 lbs

The margin for landing is:

• LW margin = 40,000 (MLW) - 40,000 (LW2) = 0

There is no weight margin for landing. Therefore if reserve fuel must be added, the payload must be reduced, and vice-versa.

However if some more fuel is required per regulation, e.g. for an alternate destination or holding, then MLW will be exceeded or you'll have to burn it before landing. Perhaps this aspect is to be ignored for your exercise, else it's a trap.

• If the flight fuel was computed for a takeoff weight of 44,000 and you add an extra 1,000 payload, you may need to account for an increased fuel burn. Oct 1 '21 at 17:50
• @Terry: That's a very good point I missed.
– mins
Oct 1 '21 at 17:52