ZFW...why

[wingzakimbo]

As en ex-dispatcher (quite a few years ago), I was trying to explain to a colleague the relationship between ZFW, MLW and MTOW.
He then asked me "why do you need to calculate the ZFW"? at which point I couldn't answer him.

Can someone enlighten me as to WHY the ZFW is used?

Thanks

[Crowsnest]

Tells the Flight Crew how much fuel they can load without going over the MTOW, Performance Limit Weight, MLW etc. Bound to be unreliable most days;)

On long sectors it would be nice to fill her up but this would result in overloading the airframe with a heavy pax/freight load. HTH.

[VIKING9]

........and you were a despatcher ???????? :rolleyes:

[wingzakimbo]

Yes...........and?


Nobody explained to me WHY, I just did as I was told. I have become wiser over the years but I am talking about a career at least 10 years ago.

[Crowsnest]

Just out of interest, in which area is your new career?

[wingzakimbo]

in air cargo. Less grief from boxes than from pax :}

[VIKING9]

wingzakimbo apologies if I came across a wee bit sarcastic but understanding ZFW is one of the very first things a despatcher should understand. I blame your previous employer for letting you down in that sense. Without a full understanding of ZFW, one really can't understand the laws behind MTOW or MLW.

Your comment "Nobody explained to me WHY, I just did as I was told" would have worried me if I had been in your shoes. If someone said to you "add that pallet to position Z, it weighs 10tons even though the position will only take 5tons", would you have done as you were told ?

I have no intention of starting an argument here, but if in that case you had done as you were told, chances are, the aircraft may not have rotated safely. The STAB trim would have been set at say 3 degrees, when it should have been at 4 degrees, especially as position Z is at the back of the aircraft. You see where I'm coming from ?

Anyway, as you say, you have become wiser over the years. Glad to hear it........:ok:

[Maude Charlee]

Don't confuse the duties of a dispatcher with those of a load controller. In some companies the dispatcher is purely responsible for supervising the turnaround, co-ordinating resources and checking the necessary paperwork is in order (ie, AAA bag numbers tally with the loadsheet, loadsheet figures tally with what was passed by the crew and load plan matches the load distribution on the loadsheet). Not all dispatchers are trained in any aspect of load control and so wouldn't need to understand the importance of ZFW.

Now if it was a pilot asking, well............!!!

[suppie]

I hope U atleast checked the DOW before U started to calculate things

[VIKING9]

Supervisor - "........yes I said position Z"...........
Despatcher - "........ok then"

Maybe I should check first ! (http://www.airliners.net/open.file/520236/L/)

[Crowsnest]

The only stupid question is the one you don't ask.:ok:

[OpsControl]

Lets start frm basics

Empty Aircraft + Pallets + Pantry = OWE
Also sometimes refered to as DOW

Add Payload ( Pax + Cgo + Crew + Baggage ) you get ZFW

Add Departure Fuel ( in tanks )
PlndRamp Out Weight

While A/c taxies out frm ramp , it burns
the taxi fuel and when it reaches end of Rwy and Intersection take off .Plnd Ramp Out Weight -Taxi Fuel
PTOW ( ZFW + T/off Fuel )

Fly Boyz perform RTOW computation based on ATIS and Airport Elevation and other performance They get RTOW ( Regulated TOW )If limiting , RTOW overrides PTOW and the necc things done .Offload cgo , Packs off T/off etc

MTOW /MLDW are aircraft certifed limits
PTOW /RTOW must not excess these limits

TOW/RTOW - Burnoff ( Trip Fuel ) = PLDW.It must not excess MLDW

Enuf said

OpsControl

[wingzakimbo]

Thanks for all replies/remarks - but I just feel I need to make a point clear, I don't want anybody to think that it was a danger being dispatched by yours truly.

I was a dispatcher and certified loadcontroller, and (for what it is worth) had done my City and Guilds dispatch/airline ops.

At that time (and we are still talking 10 years ago) I would have been able to SAFELY load and trim an aircraft in my sleep using a manual load- and trim sheet. My comment about "doing what I was told" did not mean that I didn't know what I was doing, and NO .... I would not have done anything to make a flight unsafe, I was perfectly capable of making sound judgements, and in fact pilots asked for me specifically on their turn around as they knew I would provide a safe and secure service. When doing my various courses I knew exactly WHAT the ZFW was, and the relations with all other operational weights, but I never asked WHY.

My question was spurred by a current colleagues questions of "why use ZFW, and not only TOW and LW" - I could have gone home and looked in my manuals/books/notes but needed and answer there and then.

....so in summary, all I needed was a someone to refresh my memory about WHY we use ZFW (not what it is) - )more of an existentialistic question ....this has now been done so I can answer my nosy colleague.

(but I dare say that I had dispatch colleagues who had worked for years, but still would ask questions like "what does 'in trim' mean?" ... but that is another story

[lunatismic]

Hi everyone, thought this might help:

Bending moments, which apply at the wing root, are maximum when the quantity of fuel in the wings is minimum. During flight, the quantity of fuel located in the wings, decreases. as a consequence, it is necessary to limit the weight when there is no fuel in the tanks. this limit value is called MZFW therefore the actual ZFW < = MZFW

cheers

[Captain101]

lunatismic - A point very well made

MZFW is a STRUCTURAL LIMITATION which if exceeded will mean a broken or structurally unsound aircraft.

I find it very alarming the number of dispatchers/load controllers who are unaware of this and are happily packing aircraft full of traffic load before fueling, oblivious to the damage they could be causing to the airframe.

Conveniently ZFW will tell a pilot how much fuel he can take for a given traffic load.

This is a very worrying indication of the standard of dispatch training in the UK and definatley justifies the introduction of JAA dispatch lisencing legislation.

[LHR2YYC]

Captain 101 I total agree with your coment regarding lack of training in Dispatch in Europe.As an Expat living in Canada I have both my FAA Ticket and Transport Canada.The Transport Canada isnt worth the paper its printed on.But the FAA Liscense is a good Course and its valid for Life.I hope JAA does something along the same lines.I also feel if dispatchers/Load Controlers were liscened their pay should increase to level that it deserves.US and Canada is considerble better paid for the same job than blighty.Just my $0.2

[FEBA]

Lot of bollox spoken here
It's simple - if you exceed the MZFW without fuel in the wings then the lift created will exceed the structural design loads and the wings will separate from the airframe at the wing root. See C130 on fire fighting over California C 2002
Regards
Feba

[no sig]

Its important to distinguish between the role of the 'Ramp & Flight dispatcher'. Typically the use of the term 'dispatcher' in UK refers to 'ramp' dispatch, those who work the ramp and will usually supervise the turnaround, loading, load control, boarding etc. Opposed, to the role of the Flight Dispatcher/Flight Operations Officer ( a la FAR 121 Dispatch) responsible for flight planning/operational control and for which the JAA have recently introduced the requirement to train those engaged in this role to ICAO Doc. 7192 D3 syllabus.

Now having said that, its is of course equally important that both have a clear understanding of the subject matter discussed here. Sadly, our training of both in the UK is left wanting. Captain101 has hit the nail on the head, airlines and handling agencies really do need to embrace the new training standard, and why not apply those relevent parts of 7192 D3 training to to the 'ramp dispatchers' role.

[VIKING9]

My post and picture concerning the B727 on it's ass is a serious statement. I've seen that sort of mess for real.

no sig is right, it's high time airlines, agencies etc get to grips with training and standards.

[OZBOX]

In regards to loading an a/c with pax and freight before fuelling, I see no problem with it as long as the MZFW is not exceeded (i.e. the a/c should be safe from structural damage). The only things you need to watch out for from there are that you dont exceed other structural or performance limits once fuel has been loaded, hence planned loads and the EZFW (estimated ZFW). If the flight crew reuire additional fuel due wx or alternate requirements then they can set the MZFW so we can get their fuel on.

[Irish Steve]

no sig is right, it's high time airlines, agencies etc get to grips with training and standards.

That's a lovely theory, but will the airlines then be prepared to pay the handling agents for the more skilled personnel they will then have to employ?

I would be only too happy to see a much higher skill base in all aspects of ramp handling, it would make for a much safer environment all round, but what level do you set.

I know from experience that Servisair's training covers their equipment, and some very basic fundamentals of how to use it, but there's nothing worth talking about when it comes to type specific information, which can lead to all sort of anomalies, and on occasions, serious damage to aircraft because of lack of knowledge. I've seen ATR's and Dash 8's grounded because a ramp operative didn't know that they needed a current limiting GPU for start. If things that basic are not known, what chance is there on more serious things?

Fortunately, I have other aviation experience, so I had a pretty good idea of the risks, and was able to respond accordingly.

As an example, moving the prop on (say) a completely shut down HS 748 does not present a serious risk to a ramp person. Doing the same thing on a Seneca ( to get access to the forward baggage hold) could be fatal, but nowhere do they cover those sorts of specifics.

There's a bookfull of other things that are similar, but they are ignored, and the end result is people at risk, often because of the ignorance of the management. Ideally, there should be at least one person on each shift that has a high level of aviation experience and training, but the chances of that happening are about the same as pink snow.

[no sig]

Irish Steve

It is true to say that the airlines, particularly the low cost carriers, have screwed down turnarounds costs and that handling standards have fallen. In my previous life I saw a marked increase in ground damage to aircraft, baggage and cargo mis-loading, loadsheet errors which would make you hair curl and generally a dumbing down of the ramp agents (red-caps) skills.

Much of this can be attributed to costs, but I am also of the opinion the centralised load control and computerisation of load sheets has meant that the skills and knowledge once essential to your average ramp agent have all but been lost, not in all cases of course, but in many. I am not against computerised loadsheets, far from it- in fact, if anything these prevented many errors and have increased safety. But with the likes of centralised load control etc. handling agents can save and feel they don't have to train their staff as perhaps they once would. Therein lays the danger IMHO. If an agent airside doesn't possess a sound knowledge base of the principles of aircraft loading and weight & balance = risk increases. You need only look back at some of the UK CAA FODCOMS to understand the concern within the industry over this issue, e.g.

http://www.caa.co.uk/docs/33/FOD200302.PDF

http://www.caa.co.uk/docs/33/FOD200012.pdf


Ramp safety is of course an essential and there is simply no excuse for any employee to ignore their statutory obligations in this respect. Further, the supervision of handling agents by the airline is essential and required by JAROPS1 as we all know.

Training does cost, but it needn't be a high cost and is not optional. The standards required have all been defined by the likes of IATA and ICAO and some UK NVQ's. Further, as the handling company is the agent of the airline, there is no reason why an airline shouldn't define the standards they require- easier said than done however.

[Celestar]

Lets start frm basics

Empty Aircraft + Pallets + Pantry = OWE
Also sometimes refered to as DOW

Add Payload ( Pax + Cgo + Crew + Baggage ) you get ZFW


OK I though I was an experienced (Flight Ops) Dispatcher :confused: .. and don't want to sound stupid ... but are you sure that OWE = DOW?

I understand that OWE = Empty mass ...
but for me I would say that DOW = OWE+Crew+Jeppensen+Galley storage+lavatory water+crew baggage (sometimes refered to as BOW)

[Lobotumi]

FEBA is right on both counts:

good explanation of zfw limitation, and

everything else on this thread is a load of bollocks!

Special mention though to Captain 101 - you have certainly established your credentials as a pilot ............. I haven't encountered such complete ignorance in over 20 years in the industry. (perhaps you might like to consider taking along a dog when you fly :E )

So as a dipstick check of dispatcher knowledge (or is it a dispatcher check of dipstick knowledge :{ ) ......

who can answer the following:

"when do you need to include fuel in your zero fuel weight?"

:confused:

[j_davey]

"I find it very alarming the number of dispatchers/load controllers who are unaware of this and are happily packing aircraft full of traffic load before fueling, oblivious to the damage they could be causing to the airframe."

let me interject here for a moment.... when the aircraft is on the ramp, the wings do not produce lift because the a/c aint moving... so my point is what is the problem with loading the a/c before fueling? there is no structural load placed upon the wing root(ok there is gravity:) )breaching the zfw while on the ramp will NOT cause damage provided the cargo hold weight limitations are adhered to. The ZFW only comes into play when the wings produce lift.

[VIKING9]

Lobotumi when it's being carried as ballast or dead weight. BAC1-11's (ah memories) often used fuel "trapped" in the centre tank in order to bring the C of G forward when operating empty. Once at the other end , the crew can then "untrap" the fuel and use it to get home with it's payload.

[Lobotumi]

ah Viking9 ... a little knowledge is a dangerous thing.

You are right about the 1-11 but wrong about the rest. After all if the fuel is 'trapped' then you can't use it at the other end can you? Perhaps you area bit confused with a 'short release' (and the subsequent reclaiming of reserve fuel).

'Trapped' fuel is exactly that .. trapped to ensure c of g trim at zfw (not take off weight). This was a particular difficulty of the 1-11 (especially the -300) ... when operating empty .. i.e. (to those in the know) without a 'payload'.

So .. nul points my friend. Back to the ramp for you.

:}

[VIKING9]

So how come Monarch, BIA, Dan Air to name a few, carried out that procedure as a standard practice with their -500's ? Maybe my terminology is wrong, but the fuel in the centre tank WAS used for trim purposes on empty sectors !

My days of being on the ramp are long gone my friend...... thank goodness. The job of despatcher at many airlines is not what it once was.

[Captain101]

Lobotumi-

A slice of your finest humble pie please!

I'll put my hands up to this one - I was wrong

You cannot damage an aircraft on the ramp by exceeding ZFW -
-Unless you load a low wing aircraft with a very wide main gear span to apx 3 times its Max ramp weight with zero wing fuel providing the fuselage or gear does not break first!!!

I would like to thus submit myself as living evidence of poor dispatch training in the UK along with the fact that my statement went 10 post without being corrected! The MZFW damage on the ground theory was taught to me by a dispatch trainier - I thought is was a little odd that this mode of failure was not mentioned in any of my previous training, but thought nothing of it.

From what i now understand:-
The moment created by the Fuselage weight about the main gear is reduced by the weight of fuel in the wing tank, so on the ramp with zero fuel there IS stress on the wing root - however - the wing root is capable of withstanding stress eqivallent to the aircraft undergoing it's maximum load factor (2.6g+) at MZFW with zero wing fuel. Thats quite extreme and certainly won't happen on the ground!!!

I thus retract the third paragraph of my earlier post with appologies if I mislead anyone.

[FEBA]

Viking
fuel in the centre tank WAS used for trim purposes
Don't think so old chap. Centre tank and cofg bear a healthy relationship so the influence on trim by adding fuel to it would be insignificant or very very negligable. In the case of most airliners when empty, ballast is required to improve their handling manners. I think you'll find this is why centre tank fuel was ordered for empty sectors.
As for bollox factor in this thread and the utopian ideals of my mate Nosig (how are you mate?) I note the following:
1) Technical knowledge of things structural ie ZFW and MZFW has led many to utter or pen total bollox. Bollox factor = High
2) The ideals (utopian or otherwise) of qualified or licenced dispatchers most of us share, yet collectively none of us have the balls to take action or do anything about it. My mate Nosig can exclude himself from this criticsm. Bollox factor = low
FEBA

[FougaMagister]

I agree with Maude Charlee and Captain101; and maybe, just maybe, that's why I feel that flight crew are ever so slightly more at ease with me than with some of my colleagues, since I have an ATPL (albeit still "frozen") and therefore the crew know I understand these matters.

We have indeed had an airline rep/station manager ask some of my colleagues what stab trim was, and they couldn't readily answer... I only wish he would ask me :E

It is true that in some Continental countries, the "Flight Dispatchers" are more actually called "Ground Ops Co-ordinators" and they stay with the a/c during the whole turnaround and are NOT responsible for doing the loadsheets, only for supervising loading etc.

I also agree that the responsibility to explain these definitions clearly is up to the training dept. with your handling agent - a 2-week course is nowhere near enough in this line of work.

Cheers :cool:

[no sig]

You know FEBA it still depresses me that our (UK airline industry) approach to the training of ground and ops staff is so poor and as if we needed any evidence, this post is a good example of the neglect of many of airlines and handling agents.

The only thing I would say to those out there who have not had adequate training is to ask for it- nae demand it, or if that fails go out and do it for yourself. Get the books, do the course, search the web and learn about the job. It need not lead to a Dispatchers licence (although that is a good thing) but do it for yourself. Trust me it will lead to greater job statisfaction and your advancement in the industry.

Learning on the job in our business is simply not enough, you must get the fundemental principles under your belt and the only way to do that is to STUDY. If you haven't got a training course to go to, a good place to start is with the ATPL weight and balance section of the course FougaMagister has done, then you and the crew are operating on the same level.

(FEBA old bean, hope you're well these days)

[MAN_Dispatcher]

Well from reading through the posts, it seems that the only real explanation for calculating the ZFW has been discounted....

I gathered that it was primarily for structural purposes whilst the a/c was on the ground, but there still seems to be the lack of a clear explanation for it...

[no sig]

MAN_Dispatcher

Let me have a go.

Put very simply, the maximum zero fuel weight is a structural limitation as defined by the a/c manufacturer. It is defined in the Airplane Flight Manual (for a G registered a/c the AFM is a CAA approved document) which sets out the the procedures for the safe operation of the aircraft. An airline must have a system for ensuring that limiting weights are not exceeded for each flight- in the case of MZFW it is usually by the use of a loadsheet, but can also be by the use of approved on board W&B systems. So, we need to calculate the actual ZFW for each and every flight to ensure we do not exceed the Maximum ZFW.

[FougaMagister]

I do agree with no sig, and a good point to start is either to get your hands on the Jeppesen/Oxford Mass & Balance ATPL manual or on the CAA booklet used for the actual ATPL exams - the thin yellow one, can't find it or remember what the CAP no. is! It's quite good for definitions.

In the same vein, it might be of use to follow that up with a Performance manual since a/c perf is dependent on mass and balance (along with other things such as atmospheric pressure, density alt, wind component, runway contamination, bleed air, etc).

Cheers :cool:

[FEBA]

Fouga
ZFW is a function of W&B not performance the latter, in terms of weight, concerns itself purely with mass.
To all the other confused of this site with regards to ZFW MZFW whilst the aircraft is on the ground; please consider the following:
Aircraft manufacturers and designers expect their products to spend a good deal of their useful life in the air, not on the ground. Therefor all structural restrictions concern the aircraft in the air and not on the ground (with the exception of max taxi wt, for the picky)
Man dispatcher. You may load your aircraft to the gunnels whilst on the ground without fuel in the wings, they will not fall off. However if you launch your aircraft into the air without fuel in the wings (presumably you're going to tow it into the sky) and you have exceeded the MZFW, then the wings will depart company with the fuselage at the wing root as the lever moment (created by LIFT a product which is not associated with stationary aircraft on the ground) exceeds the design loads.
This must surely be the end of this thread.
Question for the technically minded.
Take off performance - which aircraft achieved V2 before V1?

FEBA

[itsinthebox]

another question about the ZFW / ZFM debate, why plot it on the trim chart?

[Flap Sup]

itsinthebox,

You should still be able to land with dry tanks - in worst case scenario. Should you be so unlucky to divert to yr alternate, then hold for 30 mins and use your contingency fuel before landing, it would be a sad waste to crash the ac 100 feet from the runway just because of an out of trim situation.

/fs

[Craggenmore]

Question for the technically minded.

Is it the B-52 Stratofortress
:\

[FEBA]

Nope but it / was made by Boeing

[DC10 Crew]

MZFW - Maximum weight allowed before usable fuel and
other specified usable agents must be loaded in defined sections of the aircraft as limited by strength
and airworthiness requirements.

MTW - Maximum weight for ground taxi as limited by aircraft
strength and airworthiness requirements. (It includes weight of taxi and start-up fuel.)

MTOW - Maximum weight for takeoff as limited by aircraft
strength and airworthiness requirements. (This is the maximum weight at start of the takeoff run.)

[FougaMagister]

In other words, the Max Take-Off Weight is the Max Taxi Weight minus the taxi fuel.

Cheers :cool:

[DC10 Crew]

mmm! - quite correct.

But taxi fuel can be higher to give a higher than specified MTOW. and LDW, strictly Freight Dog calculation in Africa.

EZFW weight can be used for planning purposes until the AZFW is known.

:cool:

For the attention of itsinthebox

Your question another question about the ZFW / ZFM debate, why plot it on the trim chart?

It is a reference for the PIC to enter into the FMC and for the calculation of the Vr speeds. The loadsheet is a legal document and has to be anotated and signed correct by the loadmaster/dispatcher and the Captain.

Hope this helps
:D

[barit1]

I don't think this issue has been addressed:

When aux tankage is installed in the hold, shouldn't any fuel in these be counted in ZFW just as if it were cargo?

It's being carried by the spar exactly as if it were cargo.

[Opssys]

=============================================
I don't think this issue has been addressed:

When aux tankage is installed in the hold, shouldn't any fuel in these be counted in ZFW just as if it were cargo?

It's being carried by the spar exactly as if it were cargo
=============================================
Centre Tank Fuel either trapped, becuase of some defect in the
Fuel System, or when using Centre Tank Fuel as a Trim/Ballast for an empty sector, will count as load and therefore will be included as part of ZFW.

DIH

[max payload]

To think that I've worked with aircraft having a VARIABLE MZFW (B744, a fuel density thing), or NO MZFW AT ALL (DHC6 Twin Otter, a struts thing).

MZFW of course represents a manufacturer-defined limitation designed to prevent wing-fuselage joint over-stressing while operating the aircraft at maximum allowable loadfactor and at MTOW (structural), and is expressed in a (fuselage) weight limit.
The derived/designed MZFW represents a theoretical condition, and has no doubt resulted from a necessity to prevent mishandling.

Unless specifically stated otherwise in the Flight Manual, aircraft equipped with a CWT have defined/designed MZFW's that take a full CWT on departure into consideration. Contrary to ballast fuel, useable CWT fuel is therefor not part of any ZFW considerations.
Scavenge pumps INOP will cause a portion of CWT fuel to be un-useable, and therefor become ballast, however, no ZFW impact.

Non-standard fuselage AUX tanks (as in A319CJ), although representing useable fuel, should be considered to impact a ZFW.
The published MZFW should be lowered with the fuel mass loaded into these tanks when the MZFW of the original aircraft design/certification does not take fuselage AUX tank fuel into consideration, resulting in a lower max payload (pardon the pun).

... 4 pages of blissfull ignorance, blatant misconceptions, goodhearted explanations, and a lot of air- which includes this post, of course...

Cheers, Max. :ok:

[FEBA]

Nice post Max..............What's a CWT mate?

[max payload]

FEBA, good day,

CWT = Center Wing Tank.

Cheers- Max :ok:

[targaman]

If you think these postings indicate a worrying state of affairs in UK try asking a few questions of your dispatcher/loader around the international traps.

Now that will give you cause for worry!

See Tech log forum Weight & Balance enhancements.

Chok Dee

[trident3]

As an instructor of many years, I can clearly state that agents are taught that the reason for having a ZFW is to ensure that
a/The structure on the wing roots is not compromised/stressed beyond its capability if ZFW was at maximum permitted
b/At any stage of a flight, the captain uses the ZFW to determine diversion data in case of landing at unscheduled airports, usually just into flight. (ZFW plus fuel remaining = est landing weight.
.
There have been two instances whereby an aircraft has run out of fuel en route and still glided safely into land.
(Alidair Viscount-Exeter,, Air Transat-Azores.
................
Any employer using despatchers as runners for the summer season or periodically should not let them lose onto a/c until they have proven training records of understanding _theory of flight-ZFW/TOW/RLW/Loadsheet principals and 6 point check of any document handed to them to give to crew.
........
There is no legislation as to training capabilities in law yet but any good crew member may ask to see training records of any despatcher who appears to be unknowledgeable about the loadsheet/loading instructions.
.......
Who knows..It could just stop a potential incident if more challenges were made to the ground services handling agent about competency of the staff let loose to visit the flight deck!!

[Doctor Cruces]

Sorry if I haven't read through it all yet, but has anyone added the extra spanner in the works of carrying wing relieving fuel in order to get more out of the ZFW?

Doc C

[Craggenmore]

Question for the technically minded. Take off performance - which aircraft achieved V2 before V1? I have asked a number of people from Engineers to Pilots. Most people are unaware. Please spill the beans......... :p

My sanity (and others ) depend upon it......:)

Craggs

[Bumz_Rush]

On the Citation3, and perhaps others up the line there was unusable fuel, in the tanks, that was considered as ballast fuel.
Long time ago but its in the back of my mind....

Bumz

[Hyper_Dispatch]

LOL...okay..all this discussion is very interesting. So here I go. This is what I learn after being a Loadsheeter/Loadmaster/Flight Dispatcher.

DOW = Dry Operating Weight (Weight of the Aircraft/Crew/Pantry..etc..etc..But this depends also on the airlines requirement what they consider as DOW.)

+ cargo + pax + baggage + ULD's (some airlines use this as part of DOW)

ZFW = Zero Fuel Weight. (+ Block Fuel / RAMP Fuel)

= RAMP Weight (- Taxi Fuel)

= Takeoff Weight (TOW) (- Trip Fuel)

= Landing Weight (LDW)

MZFW = Maximum Zero Fuel Weight. The structural limit of the aircraft can handle.

Variable ZFW = This is usually meant for freighter aircraft like B742 or B744. What it does is basically allow the aircraft to carry more weight than the MZFW but the MTOW is greatly reduced.

MTXW = Maximum Taxi Weight

MTOW = Maximum Takeoff Weight

RTOW = Regulated/Restricted Takeoff Weight (if there is a restriction the TOW cannot exceed this weight)

MLDW = Maximum Landing Weight.

All these weights calculated in the 'loadsheet' cannot exceed these figures at any given point.

As for why plot it in the trim chart, well its to see if the weights and the position of cargo/baggage/passenger loaded in the aircraft actually 'balance' the aircraft out. As aircraft has 'curve' each weights has its own limitation hence its to ensure that both weights and the 'balance' of the aircraft is in the safety limits. Like freighter aircraft, the trim checks is to prevent 'tail-tipping' of the aircraft itself. Also, the pilots can use it for FMC for the whole flight.
:mad: