B744 Lower Cargo Loading

[xkoote 57]

Hello,

does anyone know why above certain amounts in the lower cargo hold, they become highlighted?

[Captain Kevin 586]

If I had to guess, you might be above the weight limit for the cargo hold or you may be exceeding CG limits. Not really sure what you've put in for weights or what is highlighted.

[xkoote 57]

Well I would think the same thing. However the limits are:

30270/28279/5990 in pounds. Which is 66500 pounds. I hardly think that it is all the 744 can carry in its underbelly. At LD1 max weights, that means 9 units in lower front and 8 in lower aft. The capacity is 16/14. 

Now I already know that volume capacity and floor loading are 2 different things, but the difference in full LD1 qty against volume capacity doesn't match up.

Also, there is a point where you get invalid entry in the cargo hold when you enter a value that is too high. That would probably be the load limit. But there is no desription of what the highlighted text means. I don't believe it is related to CG as it always changes at the same value. Doesn't matter in what sequence you enter them. Anything above the mentioned values turns highlighted...at any time on the ground.

 

Cheers,

[Captain Kevin 586]

I just had a look, and if you go to the payload menu on the FMC, if you hit max, you'll note that the load level reads 100% and the zero fuel weight reads 542.5. Looking at the Boeing documentation, the zero fuel weight of the standard Boeing 747-400 is, in fact, 542,500 pounds. The Boeing 747-400M appears to be 565,000 pounds, the Boeing 747-400F at 635,000 pounds, the Boeing 747-400ER at 555,000 pounds, and the Boeing 747-400ERF at 611,000 pounds. Therefore your limiting factor is the zero fuel weight.

That said, what I struggle to understand is, if your passenger count is less than the standard 416 that it allows you to put in, it won't let you load more cargo to hit the zero fuel weight. I'm not sure why that is. For instance, my Boeing 747-400 has a much lower seating capacity given the seating configuration I've devised, so I've set the passenger count accordingly (looking at the Boeing charts for the standard seating layout, I was able to figure out where first, business, and economy was in the FMC and work it out accordingly). Yet I can't load any more cargo to hit zero fuel weight because it won't let me. Or....I wonder if it would let me if I just ignored the fact that it was highlighted.

[xkoote 57]

No it's not. I can load up more than 66500 lbs of lower deck cargo and still be under MZFW. What I believe now is that if you fill the plane full of passengers, that will be the amount of cargo left over before reaching MZFW. Not sure but I'm going to check after I land. This assumes again that all seats are filled with 190 lb adults. It is probably also why you can still go over the mentioned amounts, as it only tells you that if you go over a certain amount, you can't go full adult pax anymore..

[Captain Kevin 586]

10 minutes ago, xkoote said:

No it's not. I can load up more than 66500 lbs of lower deck cargo and still be under MZFW. What I believe now is that if you fill the plane full of passengers, that will be the amount of cargo left over before reaching MZFW. Not sure but I'm going to check after I land. This assumes again that all seats are filled with 190 lb adults. It is probably also why you can still go over the mentioned amounts, as it only tells you that if you go over a certain amount, you can't go full adult pax anymore..

I think something got lost in the translation somewhere. What I intended to say is if you go to the payload menu on the FMC and you hit the max button to set the payload, you'll have all the seats filled and the cargo holds at whatever values they're set at with the zero fuel weight being at maximum. If you then try to set the cargo hold values at higher than what is there, they'll be highlighted. I don't know what passenger count you tried, but in any event, I tried clearing seats and adding more cargo, and the values for the cargo hold were still highlighted.

[xkoote 57]

Exactly, however. Those values highlight at the same values every time. Be it an empty, or partly filled cabin too as you mention. So it must be a heads up of some sorts that passing those values will limit pax load.

[Captain Kevin 586]

I'm thinking it may be a case of the FMC just using a really basic formula that doesn't take into consideration trading off passengers for cargo, therefore setting a hard limit regardless.

[VHOJT 172]

http://www.boeing.com/resources/boeingdotcom/company/about_bca/startup/pdf/historical/747-400-passenger.pdf

 

Some 744s have a higher MZFW. I've loaded up to this higher MZFW in Pmdg with no ill effects. 

[Captain Kevin 586]

Weird. Different documentation with different numbers.

[Dick 47]

That is not so weird as it seems. Airlines have a whole range of options they can buy for a certain aircraft. This could vary from cockpit of passenger (service) equipment but also different maximum weights for certain aircraft.  Many aircraft can be bought with different max zfw, different max landingweights or max tow weights . There could be a structural change involved but the airline also pays for the additional certification process. Max weights could even change during the life of the aircraft. I know of an airline that sometimes used longhaul equipment for an extended period on shorthaul flights and as landingfees etc are based on max takeoff weight they lowered the certified max tow for that aircraft for a period of time and so save on fees. You could also see other differences in aircraft. Like e.g the Md-11 can be bought with a small or large lower belly  aft door, making it possible to load pallets versus smaller luggage containers. You could also e.g see B-767 with 1 or 2 pax doors up front. All what the airlines wants and pays for and all within designs options and possibilities of course.

It also depends on what PMDG models.E.g The dc6-b comes ( as far as I understand with 10 fuel tanks ). The PMDG Dc-6 has only 8 fuel tanks as the aircraft that they modeled was apparently a   domestic version of the DC-6B with only 8 tanks.

As to your questions why weights would highlight. ( I take it you are talking about the payload screen in the FMC). Yes highlighted means you are exceeding a certain restriction. Play with the weights and you can see how the various restrictions ( like cg and gw ) interact and can be exceeded.

 

b rdgs Dick

=

 

[Captain Kevin 586]

3 hours ago, dick said:

That is not so weird as it seems. Airlines have a whole range of options they can buy for a certain aircraft. This could vary from cockpit of passenger (service) equipment but also different maximum weights for certain aircraft.  Many aircraft can be bought with different max zfw, different max landingweights or max tow weights . There could be a structural change involved but the airline also pays for the additional certification process. Max weights could even change during the life of the aircraft. I know of an airline that sometimes used longhaul equipment for an extended period on shorthaul flights and as landingfees etc are based on max takeoff weight they lowered the certified max tow for that aircraft for a period of time and so save on fees. You could also see other differences in aircraft. Like e.g the Md-11 can be bought with a small or large lower belly  aft door, making it possible to load pallets versus smaller luggage containers. You could also e.g see B-767 with 1 or 2 pax doors up front. All what the airlines wants and pays for and all within designs options and possibilities of course.

Yes, I am aware of all of that. I just find it a little unusual that two different pieces of documentation coming from the same manufacturer lists different numbers. It looks like the data Rudy was looking at came off of a brochure for the plane, and the data I was looking at was the technical data for the plane.

[xkoote 57]

Also, in this case, highlight does not seem to mean you are exceeding a restriction. Actually it seems to be telling you that may exceed the MZFW if you fill the cabin with passengers. That is all.