bio15
Posts: 1048
Joined: Fri Mar 23, 2001 8:10 am

About Landing Weights

Fri Mar 01, 2002 10:18 am

I was hoping someone could tell me which are the limitations for the landing weight. I know you can not land at MTOW. Is there some 'typical' FOB to have when landing, or it really isn't that important? (well, as long as it is below the max. obviously)
Thanks in advance, hope my question is clear.

-bio
 
AJ
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Joined: Wed Nov 03, 1999 3:54 pm

RE: About Landing Weights

Fri Mar 01, 2002 10:31 am

Bio,
The maximum landing weight (MLW) for a specific aircraft is a fixed figure from the aircraft's limitations manual. This weight is made up from the aircraft's 'zero fuel weight' and the remaining fuel in tanks. The aircraft manufacturer specifies this weight depending on customer specifications.
Some aircraft with a large split between Maximum Takeoff Weight and Maximum Landing Weight have a fuel jettison system to allow a reduction in the aircraft weight down to MLW.
If an aircraft lands above this weight an inspection must be carried out causing unwanted downtime.
The amount of fuel in the tanks on landing depends on the operation of the day. A minimum amount would be just reserve fuel, however sometimes the aircraft will land heavier due to unused weather/traffic holding fuel, or the company is 'tankering' fuel to a place with poor fuel supplies, or simply due to fuel costs.
Even when tankering the weight is not necessarily taken to MLW due to the increased brake and tyre wear of the higher speed landing.
Hope this helps, I can get more technical on certain aspects if you require!
 
ramper@iah
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RE: About Landing Weights

Fri Mar 01, 2002 11:14 am

On short trips, the aircraft's takeoff weight is actually limited by its landing weight. For example, if an aircraft's max takeoff weight is 37,258, and the max landing weight is 36,160 and the fuel burn to the destination is less than 1,098 (37,258 - 36,160 = 1,098), then the burn, let's say 600 pounds, would have to be added to the max landing weight to get the max takeoff weight. This limitation would be "landing structual." When the burn is more than 1,098 (in this particular situation), then the aircraft would be "takeoff structual." That means the aircraft could be loaded to the maximimum gross takeoff weight.
 
bio15
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RE: About Landing Weights

Fri Mar 01, 2002 11:17 am

Yes thanks.
But to see if I got it right, the optimum tankering would be to tank in order to land on reserves, for saving tire wear or fuel expenses?
-bio
 
radarbeam
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Joined: Fri Mar 01, 2002 9:00 am

RE: About Landing Weights

Fri Mar 01, 2002 12:27 pm

Hello Bio,

Actually, some aircrafts are designed so they can land at their MTOW, of course most of those aircrafts are GA planes.

Radarbeam
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: About Landing Weights

Fri Mar 01, 2002 2:36 pm

"Bio,
The maximum landing weight (MLW) for a specific aircraft is a fixed figure from the aircraft's limitations manual. This weight is made up from the aircraft's 'zero fuel weight' and the remaining fuel in tanks."

The first sentence is correct, the second doesn't make sense and is therefore wrong. Max landing weight is the max weight at which the a/c can land; obviously it includes fuel, a/c BOW, AND payload.

There is NO such thing as Zero Fuel Weight in the regs. One can define it for a specific airframe, but it doesn't pertain to a/c performance limitations.

MAX Zero Fuel Weight, which simply means that any weight added to the airframe at that point MUST be in fuel....is a limitation.

For a 121 operation, one has to land with the fuel that is specified in the release, modified in flight according to whether the a/c held, was diverted to the alternate, is tankering fuel, MELs, etc.

Around 3500lbs on arrival is approximate for most domestic RJ operations; whereas 3500 lbs probably wouldn't cover the fuel suctions in a 747-400, so obv it varies w/ airframe, FAA part, wx, MEL lists, etc...
 
AJ
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RE: About Landing Weights

Sat Mar 02, 2002 7:32 am

Actually EssentialPowr, if you've ever operated an FMC equipped aircraft the performance initialisation page requires a zero fuel weight from the load sheet, which the FMC then adds to the FMC derived fuel load to give the aircraft's gross weight at any time during the flight.

"There is NO such thing as Zero Fuel Weight in the regs. One can define it for a specific airframe, but it doesn't pertain to a/c performance limitations." - I never said it was from the regs. The statement is simply an application of data entered into the FMC to allow calculation of the aircraft's Landing Weight to ensure compliance with the Maximum Landing Weight, be it the aircraft limitation of a Field Limit Weight. The FMC can forecast fuel in tanks on arrival, which when added to the ZFW (which doesn't change during flight), gives the forecast landing weight.

"The first sentence is correct, the second doesn't make sense and is therefore wrong." - watch out for statements like this.
 
bio15
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RE: About Landing Weights

Mon Mar 04, 2002 3:30 am

Thanks, I sort of got the idea!
-bio
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: About Landing Weights

Tue Mar 05, 2002 1:16 pm

AJ,

What weight does that page bring up? The BOW; unique to the tail #. Who cares about what the FMC says, or if the a/c even has an FMC? Do the math the old fashioned way; whether or not the a/c has an FMS doesn't matter in the least...MGLW is a certified limit; max landing weight as you state means nothing.

You stated "The maximum landing weight (MLW) for a specific aircraft is a fixed figure from the aircraft's limitations manual. This weight is made up from the aircraft's 'zero fuel weight' and the remaining fuel in tanks."

Where's the payload? Forget the FMS. If the BOW of tail #453 is 125,386 lbs, with 8000 lbs of fuel, what is the value of adding those numbers? Nothing. Who flies an a/c and fuel, only, to a destination (and stays in business). No one. I'm sure every airline flying into Newark would like for Port Authority landing fees to be calculated as you describe; unfortunately; they're based on MGLW, since that includes payload.

You omitted Payload with an inaccurate definition, and then rationalized it by referencing the "FMS" (???). MGLW has been around a long time before FMSs, and to my knowledge-

the math hasn't changed...
 
EssentialPowr
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Joined: Wed Sep 06, 2000 10:30 pm

RE: About Landing Weights

Tue Mar 05, 2002 1:24 pm

One other thing.

MGLW is MGLW; how ever the operator chooses to arrive at that value; so be it. Typically, a landing weight includes payload; MGLW is a certified limit.
 
AJ
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RE: About Landing Weights

Wed Mar 06, 2002 8:56 am

Feisty to the point of nasty.
A zero fuel weight includes aircraft basic empty weight plus all payload. It is exactly that, the weight of the aircraft fully loaded sans fuel.
Many aircraft have a ZFW weight limit due to structural limitations, especially wing bending moment with wing mounted main gear.
I choose to put down what I know, and at the moment my knowledge is right up there with aircraft fitted with FMCs. Please feel free to add knowledge from your area of expertise, but back off with the attacks.
 
EssentialPowr
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RE: About Landing Weights

Fri Mar 08, 2002 1:37 pm

Exactly the contrary. I stated you were wrong and explained why. The MAX landing weight is a LIMIT, it is not a variable value.

As you put it, BOW + FOB = MLW. This is incorrect; as the BOW and FOB do not necessarily equal MLW. In fact, for any case in the US, to be legal, BOW + FOB must be less than or equal to MLW. THAT IS WHAT you should have stated; particularly if you claim to know the material.


So, per your request, I'll add to the discussion.
Specific to the US and per FAA part 121, a/c are dispatched to domestic destinations in the US, excluding ETOPS or terrain clearance, subject to the following 6 limitations. The maximum takeoff weight is the minimum of the following 5 constraints, in addition to the 6th:

1. Max Ramp Weight - taxi fuel
2. MGTOW (structural t/o weight)
3. Runway Limit
4. Climb Limit
5. Max Structural landing weight + fuel burn

6. The a/c cannot be loaded such that the Max Zero Fuel Weight is exceeded. This limit means that any weight placed on the a/c above this limit MUST be in fuel to minimize wing bending moments.

These are the equations that accuload or the FMS, or a 2nd officer does in pen and ink. Not every airline uses a "Load sheet"...

Regardless, the above equations and logic form the basis of the "FMS performance initialization" to which you refer...as I said, it's basic math.
 
AJ
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RE: About Landing Weights

Fri Mar 08, 2002 4:57 pm

You are definately confusing matters.
"As you put it, BOW + FOB = MLW" - Huh? That is not what I stated. Are you confusing BEW with BOW?
I have stated that the aircraft weight consists of BEW+Payload+Fuel at any time during the operation. On landing the BEW+Payload will (almost always) be the same, only the fuel is a variable. Although the FARs and CARs vary with definitions this is fact.
In response to Bio's question I cannot categorise Colombian regulations, so I have used Australian as an example to answer his specific question.
I am sure that carrying on like this is not clarifying matters for him.
 
EssentialPowr
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RE: About Landing Weights

Fri Mar 08, 2002 6:36 pm

Are you kidding??? That's exactly what you stated. Your exact quote:
"Bio,
The maximum landing weight (MLW) for a specific aircraft is a fixed figure from the aircraft's limitations manual. This weight is made up from the aircraft's 'zero fuel weight' and the remaining fuel in tanks."

Algebraically, you are stating: MLW = ZFW + Fuel in tanks (FOB). For the 4th time, This is Not a True Statement. The CORRECT statement is FOB + BOW must be LESS THAN or Equal to MLW, with (BOW=a/c + payload). There is huge difference b/t the 2 statements...

Further, the statement "On landing the BEW+Payload will (almost always) be the same, only the fuel is a variable" is inaccurate as well. Payload can vary greatly from trip to trip.

His question was, effectively, "What is the landing weight restriction?" You started to answer it, but botched it up. I clarified it, noting that FMSes simply automate the above equations listed above, and amplified it by providing the other restrictions that can limit take off weight in ADDition to Max Landing Weight.



 
AJ
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RE: About Landing Weights

Sat Mar 09, 2002 7:39 am

.
 
bio15
Posts: 1048
Joined: Fri Mar 23, 2001 8:10 am

RE: About Landing Weights

Sun Mar 10, 2002 3:04 am

I'm not all that knowledgeable, but I seem to find both your arguments the same - I got the idea. Thanks for going beyond answering the original question, it's interesting data! Although I would appreciate if you specified what BOW stands for (the acronym, cause I know it's a/c+payload), and BEW.

I'm not familiar with any Colombian regulations, all I know is some aircraft will get to depart under MTOW when they fly to poorly fuel supplied airports. Those takeoffs at El Dorado with a heavy a/c are quite some long rolls! enjoyable...

-bio
 
Loadcontroller
Posts: 84
Joined: Wed Feb 06, 2002 5:24 am

RE: About Landing Weights

Sun Mar 10, 2002 7:37 am

Radarbeam

Don't tell us bullshit in a technical forum. NO aircraft can land with its maximum take off weight. For example: A Swissair A320-214 MTOW is 73500 kgs. The maximum landing weight is 64500 kgs and it is for all aircrafts similar.

EssentialPowr

Tell me the airline who takes off without loadsheet and they will stop operating next minute. Some pilots do a loadsheet by themselves but they would never take off without knowing what is loaded where on their aircraft.

Both is my daily business.......

Loadcontroller
 
AJ
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RE: About Landing Weights

Sun Mar 10, 2002 9:30 am

You're welcome Bio, sorry if it led to some confusion.
 
FredT
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RE: About Landing Weights

Sun Mar 10, 2002 9:45 am

Stating that NO aircraft can do this or that is a very dangerous thing. Most if not all aircraft can land with MTOW - the degree of inspection necessary afterwards is varying though. There are also plenty of aircraft capable of landing at MTOW with no inspection required. You don't even have to go down to the GA world. I found the 717-200 after a quick search and there should be more.

Sorry, but I have this allergy to blanket statements.  Smile

Cheers,
fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
EssentialPowr
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RE: About Landing Weights

Sun Mar 10, 2002 9:56 am

Loadcontroller-

Ever heard of ACARS?

At least 3 of the top 6 airlines in the US use ACARS/Accuload via a load planning office and associated link.

The flight crew for these airlines typically NEVER do ANY hardcopy mathematical calculations. Hardcopy performance numbers are pen and ink changed if a new MEL occurs, if weather or pax loads change significantly, etc...

If "Both IS your daily business" then you obviously don't know how US airlines do it.
 
EssentialPowr
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RE: About Landing Weights

Sun Mar 10, 2002 10:00 am

To add to Fred T-

Several 727-200s from an airline that became defunct in the 80s were sold to a current top 5 US airline. The Max Landing Weights on these a/c were increased by around 7,500 lbs. The certification was only a PAPER WORK drill (new STC), along with a fee paid to Boeing, of course...Nothing was physically touched on the a/c.
 
kellmark
Posts: 542
Joined: Thu Dec 21, 2000 12:05 pm

RE: About Landing Weights

Sun Mar 10, 2002 10:52 am

Wow, what a lot of emotion here.

I just wanted to add that there are other landing restrictions to think about besides the structural landing weights which nobody has talked about.

Here is how it normally works.
1. Structural landing weght- usually a fixed number.
2. Field length limit- the requirement of the aircraft to land and stop in 60% of the runway length and any stopway. This can be restrictive in a short runway situation. Also sensitive to wind factors, slope, etc. When the runway is wet, increased by 15%.

3. Approach climb limit. Requires the ability to make a go around with the aircraft in approach configuration- approach flaps, gear up, one engine inop.

4. Landing climb limit. Requires the ability to make a go around in the landing configuration- gear down, landing flaps and all engines operating.

Both Approach and landing climb limits can be restrictive at high altitude airports. Sensitive to temperature values.

Anyway, the lesser of all of these is what determines the actual maximum landing weight, with adjustments for any MELs, such as an antiskid inoperative, which can effect significantly the field length limit.

Best Regards.

 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: About Landing Weights

Sun Mar 10, 2002 2:27 pm

I would add that for Approach Climb and Landing Climb, power is assumed to be takeoff thrust for the remaining engines, or takeoff thrust on all engines, respectively.

For Approach Climb, gradients are assumed to be 2.1% for 2 engine, 2.4% for 3 engine, and 2.7% for four engine a/c.
For Landing Climb, the gradients are 3.2% for 2,3 or 4 engine a/c.

The 6 limits I offerred were for the takeoff scenario...
 
radarbeam
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Joined: Fri Mar 01, 2002 9:00 am

RE: Loadcontroller

Sun Mar 10, 2002 3:50 pm

Loadcontroller,

Hey buddy, read my post again. I talk about GENERAL AVIATION, C152 MTOW is 1670 lbs and it's MLW is the same. C172 MTOW is 2400 lbs and MLW is the same. Don't beleive me? Read up their POH's. Don't be so quick to jump on the gun.

Radarbeam
 
EssentialPowr
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Joined: Wed Sep 06, 2000 10:30 pm

RE: About Landing Weights

Mon Mar 11, 2002 12:14 am

Radarbeam is Exactly right as well...Loadcontroller doesn't know as much as he thinks.
 
Loadcontroller
Posts: 84
Joined: Wed Feb 06, 2002 5:24 am

RE: About Landing Weights

Mon Mar 11, 2002 6:07 am

We also use ACARS, for shure I heard about it. And we send the loadsheets into the cockpit of the respective aircraft. But it still gets a loadsheet. Also I produce loadsheets for AA and DL. Even though I work in Switzerland, they want loadsheets.

Sorry please, I did not want to offend any member of this forum. I made a mistake by saying NO to all aircrafts. An aircraft can achieve its weightlimits in the MTOW and the MLW at the same time, thats correct. But I cannot imagine how it should land with the MTOW, because it wouldn't burn any fuel then. And anyway, can somone explain why aircrafts dump fuel before an unplanned landing? Might it be because it is too heavy, mabe even over the MLW...
 
Mike Papa
Posts: 1
Joined: Mon Jan 28, 2002 12:22 pm

RE: About Landing Weights

Thu Mar 14, 2002 1:09 pm

Just to add some information for Bio15...this is my knowledge based on certain carriers, and I'm not claiming this is authoritative (ie. please correct any inaccuracies if you find them).

Weight build-up generally follows these steps:

* Start with the Basic Weight of the aircraft. The Basic Weight is the weight of the empty aircraft as weighed by the manufacturer. The airline might make structural changes or other changes like adding galleys and so on. All these changes must be included in the Basic Weight (and index, obviously, but I won't go into index effects here as the initial question was about weights only). This Basic Weight includes seats, cabin fittings etc.

* Add the weight of any service weight adjustments, such as stretchers, flight spares, etc.

* Add the weight of crew, crew bags and pantry.

* Add the weight of any trapped or ballast fuel. This is fuel that will not be used.

* You now have what is known as the Dry Operating Weight. (DOW).

* To the DOW, add the weight of deadload (cargo, pax bags, etc) and add the weight of the pax themselves. Early in the piece you'll have estimated figures, but as the pax start checking themselves and their bags in, you'll start to get actual data.

* You now have the Zero Fuel Weight (ZFW). There will be a maximum ZFW (MZFW) as defined by the manufacturer. Obviously you should check your ZFW is less than your MZFW.

* To the ZFW add the usable fuel weight, including taxy fuel. You now have a Ramp Weight (also sometimes called Taxy Weight).

* The aircraft will burn some fuel when taxying. So the Takeoff Weight = Ramp Weight - Weight of Taxy Fuel burned. Usually this is an approximation, but the amount of Taxy fuel allowance might change depending on the airport. Some large airports require a long taxy.
Again there is a manufacturer or carrier imposed Maximum Takeoff Weight (MTOW) which the actual TOW should be less than.

* During flight, the trip fuel will burn off. So your Landing Weight will usually equal your Takeoff weight minus trip fuel burned. There are too many variables in fuel burn to really accurately calculate this before the flight (ie. on the ground before departure). It's usually worked out by the FMC as that will have fairly accurate fuel usage information as the aircraft burns fuel off during flight. The way the FMC might work it out is ZFW plus the weight of remaining fuel in tanks at landing. I'm not sure of the workings of FMCs so I won't comment, but ideally these two calculations will produce the same result

* Again there will be an imposed Maximum Landing Weight which ideally should not be exceeded. However in some emergency situations where there hasn't been enough time to dump fuel, the aircraft may have to land over it's max landing weight. This may put excessive stress on the undercarriage and other structures, as well as brakes / tyres.

Comments welcome.

MP
 
bio15
Posts: 1048
Joined: Fri Mar 23, 2001 8:10 am

Exceding Mzfw

Tue Mar 19, 2002 10:13 am

Lots of interesting information, thanks again.

Is there a possiblity of the MZFW being exceeded? Given the case, if ZFW includes pax and pax bags load, is there a chance that people may have to be loaded off the aircraft?

-bio
 
AJ
Posts: 2295
Joined: Wed Nov 03, 1999 3:54 pm

RE: About Landing Weights

Tue Mar 19, 2002 11:38 am

Yes, MZFW can be exceeded, especially when operating short haul in long haul aircraft. This is due to the aircraft MZFW being designed around carrying a lot of fuel, and instead the operator chooses to operate high load, short distance flying.
An example of this is the Boeing 767-338ERs operating Sydney-Melbourne sectors in Australia.
All limitations in aviation must be respected and adhered to!

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