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About Landing Weights  
User currently offlineBio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7
Posted (12 years 6 months 3 weeks 5 days 22 hours ago) and read 2963 times:

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

28 replies: All unread, showing first 25:
 
User currently offlineAJ From Australia, joined Nov 1999, 2391 posts, RR: 24
Reply 1, posted (12 years 6 months 3 weeks 5 days 21 hours ago) and read 2839 times:

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!


User currently offlineRamper@IAH From United States of America, joined Dec 2001, 240 posts, RR: 1
Reply 2, posted (12 years 6 months 3 weeks 5 days 21 hours ago) and read 2800 times:

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.

User currently offlineBio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7
Reply 3, posted (12 years 6 months 3 weeks 5 days 21 hours ago) and read 2784 times:

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


User currently offlineRadarbeam From Canada, joined Mar 2002, 1310 posts, RR: 4
Reply 4, posted (12 years 6 months 3 weeks 5 days 19 hours ago) and read 2769 times:

Hello Bio,

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

Radarbeam


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 5, posted (12 years 6 months 3 weeks 5 days 17 hours ago) and read 2757 times:

"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...


User currently offlineAJ From Australia, joined Nov 1999, 2391 posts, RR: 24
Reply 6, posted (12 years 6 months 3 weeks 5 days ago) and read 2734 times:

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.


User currently offlineBio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7
Reply 7, posted (12 years 6 months 3 weeks 3 days 4 hours ago) and read 2693 times:

Thanks, I sort of got the idea!
-bio


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 8, posted (12 years 6 months 3 weeks 1 day 19 hours ago) and read 2675 times:

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...


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 9, posted (12 years 6 months 3 weeks 1 day 19 hours ago) and read 2670 times:

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.


User currently offlineAJ From Australia, joined Nov 1999, 2391 posts, RR: 24
Reply 10, posted (12 years 6 months 3 weeks 23 hours ago) and read 2637 times:

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.


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 11, posted (12 years 6 months 2 weeks 5 days 18 hours ago) and read 2602 times:

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.


User currently offlineAJ From Australia, joined Nov 1999, 2391 posts, RR: 24
Reply 12, posted (12 years 6 months 2 weeks 5 days 15 hours ago) and read 2593 times:

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.


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 13, posted (12 years 6 months 2 weeks 5 days 13 hours ago) and read 2587 times:

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.





User currently offlineAJ From Australia, joined Nov 1999, 2391 posts, RR: 24
Reply 14, posted (12 years 6 months 2 weeks 5 days ago) and read 2563 times:

.

User currently offlineBio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7
Reply 15, posted (12 years 6 months 2 weeks 4 days 5 hours ago) and read 2537 times:

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


User currently offlineLoadcontroller From Switzerland, joined Feb 2002, 85 posts, RR: 5
Reply 16, posted (12 years 6 months 2 weeks 4 days ago) and read 2531 times:

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


User currently offlineAJ From Australia, joined Nov 1999, 2391 posts, RR: 24
Reply 17, posted (12 years 6 months 2 weeks 3 days 22 hours ago) and read 2522 times:

You're welcome Bio, sorry if it led to some confusion.

User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 18, posted (12 years 6 months 2 weeks 3 days 22 hours ago) and read 2521 times:

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.
User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 19, posted (12 years 6 months 2 weeks 3 days 22 hours ago) and read 2519 times:

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.


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 20, posted (12 years 6 months 2 weeks 3 days 22 hours ago) and read 2514 times:

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.


User currently offlineKellmark From United States of America, joined Dec 2000, 693 posts, RR: 8
Reply 21, posted (12 years 6 months 2 weeks 3 days 21 hours ago) and read 2514 times:

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.



User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 22, posted (12 years 6 months 2 weeks 3 days 17 hours ago) and read 2505 times:

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...


User currently offlineRadarbeam From Canada, joined Mar 2002, 1310 posts, RR: 4
Reply 23, posted (12 years 6 months 2 weeks 3 days 16 hours ago) and read 2501 times:

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


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 24, posted (12 years 6 months 2 weeks 3 days 8 hours ago) and read 2491 times:

Radarbeam is Exactly right as well...Loadcontroller doesn't know as much as he thinks.

25 Loadcontroller : 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.
26 Mike Papa : 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 correc
27 Bio15 : 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
28 AJ : 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
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