MAX TOW value

SimBrief Dispatch
1

Hello. When creating a FPLN, in page 3 appears a WEIGHTS section.
In TOW row, there is a correct EST value, but I do not understand the MAX value, followed by “LDG” word. Shouldn´t it be the same as MTOW given in page 1?
Otherwise, how is POSS EXTRA calculated?
I am using a A320 NEO airframe.
Thank you and regards.

2

Hi, the MTOW on page 1 is the “Structural” MTOW.

The MTOW on page 3 is sometimes lower in order to make sure you do not exceed the MLW at destination.

For example, on your latest flight, the planned fuel burn was 2091 kg, and the aircraft’s MLW (Max Landing Weight) is 67400 kg. That means that if you take off any heavier than 69491 kg, you won’t burn enough fuel and will end up landing over your MLW. So the system caps the TOW to 69.5, and shows this on page 3 with “LDG” next to it (indicating that the limiting factor is the MLW).

The POSS EXTRA is also linked to this. So POSS EXTRA will be either the amount of room left in the tanks, or the amount of fuel you can add before you reach the MTOW on page 3 (whichever is lower).

Best regards,

3

Thank you for the answer, is perfectly clear now.
En 29 nov. 2021, en 22:09, SimBrief via Navigraph <navigraph1@discoursemail.com> escribió:

4

Hi, Simbrief.
Sorry for reopening this topic, as I had recently studied it closely and if I understand well there are 3 limiting TOWs (bracketed my flight values in Kg):

  • MTOW (79000)
  • MLW + TRIP FUEL (67400 + 2091 = 69491)
  • MZFW + T/OFF FUEL (64300 + 5181 = 69481)
    Shouldn´t it be MZFW limiting the MTOW to 69481 in this case?
    Kind regards.
5

I’m not sure I understand your question to be honest, but the MZFW is not affected by fuel at all. You’ll never exceed the MZFW by adding more fuel, since by definition it’s the weight of the aircraft without fuel.

In that example, there’s nothing about the MZFW that’s limiting your TOW. You’ve maxed out the ZFW portion since you’re at MZFW (64300), but nothing is stopping you from adding more fuel and increasing your TOW that way.

To think of it another way: If we ignore the MLW entirely, nothing would stop you from taking off at MTOW (79000). You could add payload up to MZFW (64300) and then add 9000 kg of extra fuel on top of that to bring the total takeoff fuel to 14700 kg. The reason you can’t do that is you would land way over MLW when you arrive, therefore the MLW is limiting.

Hope that helps,

6

Sorry to disagree with you.
I assisted to a W/B course years ago, and if I remmeber well, there were 3 limiting TOW at takeoff runway:

  • MTOW itself
  • MLW + TRIP FUEL (as you correctly said, to not exceed MLW at landing)
  • MZFW + T/O FUEL (in case you run out of wing fuel during flight, the aircraft weight would be at a ZFW state, and exceeding structural MZFW)
    This latter could be the limiting one, as apparently happens in my last flight.
    Please check this issue, it seems important IMHO.
    Regards.
7

I don’t understand your logic here, it almost sounds like you’re only considering the TOW increase due to payload. But don’t forget that TOW can also be increased with fuel as well. Let’s do an experiment, ignoring the MLW limitation again:

In your flight: MZFW + T/OFF FUEL = 64300 + 5181 = 69481. So you are saying we cannot take off heavier than that, because we would exceed the MZFW.

That’s just not how that works, you could simply add 5000 kg of extra fuel, making your block fuel 10181 and keeping the same ZFW, resulting in the following: 64300 + 10181 = 74481.

We have now magically increased our TOW to 74481 kg, yet still haven’t exceeded either the MTOW or MZFW. If you ran out of fuel in the second case, it means you’ve burned 10181 kg of fuel instead of 5181. In both cases, with tanks empty, your weight is still respecting the MZFW of 64300.

So yes, the MZFW does limit the amount of extra payload we can take. But it does not stop us from adding extra fuel, and increasing the TOW that way. On the other hand, the MLW at destination is preventing us from taking off any heavier than 69491 kg, therefore that is the limiting factor.

If there was a limiting code next to the PAYLOAD line of the OFP, then I agree, MZFW would be limiting for that line. But we’re talking about the limiting code next to the TOW.

Perhaps you’re thinking of an aircraft-specific restriction of some kind. If so, you’ll need to be much more specific, at the very least including the aircraft type you’re referring to please. Then I can look into it more closely.

8

Good morning, Simbrief.
I think you are right, I am sorry for insisting on this. I was mixing up things, what I was showing is the MTOW for that given amount of FOB, which allows to calculate the maximum payload that can be carried. Nothing to do with maximum fuel obviously.
My apologies and thank you for your full detailed explanation.
Otherwise an excellent software, essential for flight simulators.
With regards,
Ricardo

9

No problem Ricardo, glad to help!

Best regards,

Derek

10

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