Boeing 737 dumps fuel, fearing...

[Calfo]

...brake trouble!

By The Canadian Press<table class="ad_slug_table" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td align="center"><object classid="clsid<img src=" images="" smilies="" icon_biggrin.gif="" alt="" title="Very Happy" smilieid="3" class="inlineimg" border="0"> </object><noscript> </noscript>
</td></tr></tbody></table><script language="javascript"> f(window.yzq_d==null)window.yzq_d=new Object(); window.yzq_d['sYxtN9G_fyk-']='&U=13b5f5tcu%2fN%3dsYxtN9G_fyk-%2fC%3d607575.12221386.12631230.7707862%2fD%3dLREC%2fB%3d5195916'; </script><noscript>http://row.bc.yahoo.com/b?P=J.H0wdG_RzTRiiV6Rz4MGAiAS51PO0e_E0gAAl.S&T=13v6vn8ql%2fX%3d1203704649%2fE%3d96400489%2fR%3dca_news%2fK%3d5%2fV%3d2.1%2fW%3dHR%2fY%3dCA%2fF%3d2234940285%2fQ%3d-1%2fS%3d1%2fJ%3d3E46BFD1&U=13b5f5tcu%2fN%3dsYxtN9G_fyk-%2fC%3d607575.12221386.12631230.7707862%2fD%3dLREC%2fB%3d5195916</noscript>OTTAWA - A First Air passenger jet with 42 passengers on board has landed safely after dumping fuel as it circled Ottawa International Airport.

The precaution was ordered after the flight crew reportedly told air traffic controllers the Boeing 737 may have a problem with its brakes.

The aircraft began to dump fuel before attempting a landing, a tactic experts say it not uncommon in such a situation.

First Air services 25 northern communities with connections to Ottawa, Edmonton, Winnipeg and Montreal.

http://ca.news.yahoo.com/s/capress/ottawa_airplane

EDIT: oops, maybe I should of posted this in the Aviation Safety forum.

[Rolling-Thunder]

Makes perfect sense to me !

Less weight, shorter landing roll, less brake force required to stop plane, less heat generated by pads/rotor, etc.

[Kjell Engkrog]

Is the 737 (any series) capable of dumping fuel?

[juan23]

That's odd ...............................737's don't have a fuel dump capability.......

[pkonowrocki]

First Air uses old 732s, maybe those do have a fuel dump capability,
or maybe it was a 723, just a spelling mistake in the article or authors mistake ?

[Kjell Engkrog]

723? 727 was only produced in -100 and -200 series. AFAIK no 737 had/has fuel dump capability.

[flyboy2548m]

First Air uses old 732s, maybe those do have a fuel dump capability,


Uh, no.


or maybe it was a 723, just a spelling mistake in the article or authors mistake ?

What in blazes is a 723?

[juan23]

NO 737's have a dump capabilityWhat the silly media person probably did was assume that it was dumping fuel as it circled, it was probably circling in a high drag configuration at a high power setting, and burning off the fuel at a higher than normal rate

[Kell Kong]

Why are you all doubting guys??? If a tactic expert :mad: says so... this was then an ordered precaution...Since when pilots are ordered to do??? and by whom??


Just a bunch of nonsense..

The aircraft circled around in order to burn fuel and reach its maximum landing weight, MLGW.. That is not to have better braking effectiveness or whatsoever, but that is the limit over which you damage your aircraft structurally if you land it.. If you must interrupt your flight but there is no need for landing ASAP, just burn the fuel..

That is the normal SOP the tactic expert :-x refers to...

[767 Driver]

Why are you all doubting guys??? If a tactic expert :mad: says so... this was then an ordered precaution...Since when pilots are ordered to do??? and by whom??


Just a bunch of nonsense..

The aircraft circled around in order to burn fuel and reach its maximum landing weight, MLGW.. That is not to have better braking effectiveness or whatsoever, but that is the limit over which you damage your aircraft structurally if you land it.. If you must interrupt your flight but there is no need for landing ASAP, just burn the fuel..

That is the normal SOP the tactic expert :-x refers to...

If you land with a normal or lower than normal descent rate (300 fpm or less) you SHOULD not structurally damage the aircraft. When they certify transport category airplanes, they are certified to land up to their max structural takeoff weight.

[T.O.G.A.]

I wonder how they knew they had brake troubles in flight?

[pkonowrocki]

What in blazes is a 723?
As set of three numbers in no particular order.. :skeptic:
Why are you all doubting guys???
They'r all experts, you know engineering Ph.Ds.. :uhoh:

[Kell Kong]

If you land with a normal or lower than normal descent rate (300 fpm or less) you SHOULD not structurally damage the aircraft. When they certify transport category airplanes, they are certified to land up to their max structural takeoff weight.

That is not entirely true, fuel jetison systems are not only here for cosmetics. If you refer to smaller and lighter planes, it is a manufacturer's decision to simplify the system and thus saving weight, by not installing jettison system, considering the small margin between max take off weight and max landing weight.. It is of course different on each type, but for instance the A320 basic, MTOW is 68000 and MLGW is 63000 (KGS).

[767 Driver]

That is not entirely true, fuel jetison systems are not only here for cosmetics. If you refer to smaller and lighter planes, it is a manufacturer's decision to simplify the system and thus saving weight, by not installing jettison system, considering the small margin between max take off weight and max landing weight.. It is of course different on each type, but for instance the A320 basic, MTOW is 68000 and MLGW is 63000 (KGS).

There is no fuel jettison system on the 757 where the MTOW is around 115K KGS and MLW is around 95K KGS. So, saying it's only "smaller" airplanes without fuel jettison systems is not entirely true.

[AJ]

We have 767s with 185,000kg MTOWs and 145,100kg MLWs and no fuel dump capability!

[767 Driver]

We have 767s with 185,000kg MTOWs and 145,100kg MLWs and no fuel dump capability!

Are those earlier -300 models? Our -300's have fuel dumping (center tank only). We have one model that has a MTOW of 186,880 KGS and the rest have MTOW of 185,000kg and 145,000kgs MLW

[AJ]

Are those earlier -300 models? Our -300's have fuel dumping (center tank only). We have one model that has a MTOW of 186,880 KGS and the rest have MTOW of 185,000kg and 145,000kgs MLW
Yeah, 1988 -338(ER) models (cn24146, cn24316, cn24317).

[Gabriel]

FAR 25 requires that an aircraft must be able to land at MTOW without damage. Only that the vertical speed at touchdown that the aircraft is required to be able to withstand is less for a MTOW landing than for a MLW landing.

However, AFAIK the standard procedure is, if not in big hurry, burn/dump fuel to reach MLW before landing.

[flyboy2548m]

FAR 25 requires that an aircraft must be able to land at MTOW without damage.

No, it doesn't. There are plenty of qualifiers there. Refer to 25.723, .473 and .479.

[Dmmoore]

No, it doesn't. There are plenty of qualifiers there. Refer to 25.723, .473 and .479.

Unless the aircraft is equipped with a device that prevents a descent rate at touchdown of less than 6 FPM Gabriel is correct.

The landing gear must be able to support the aircraft at MTOGW + a 6 FPM rate of descent increment and a 25% drag factor. Both of the above additions can be modified if it can be shown the aircraft can not reach these limits. Anyone know of a commercial aircraft not subject to the full limit without decrement?

[flyboy2548m]

Unless the aircraft is equipped with a device that prevents a descent rate at touchdown of less than 6 FPM Gabriel is correct.



That's not quite what the FAR reads, is it, Don? Nor is the term "no damage" found anywhere therein, is it? And if you can hold 6FPM at landing, you're a better pilot than I am, which I highly doubt. Better wrench, maybe, but better pilot, not likely.

[Kell Kong]

There is no fuel jettison system on the 757 where the MTOW is around 115K KGS and MLW is around 95K KGS. So, saying it's only "smaller" airplanes without fuel jettison systems is not entirely true.

I think I remember saying it is up to the manufacturer...But sorry I should rather say it's depending if they can demonstrate that airplane can land with maxi takeoff weight without breaking out..

However, I maintain that this is a no, no... It is not a normal procedure to land over your MLGW... Only if captain decides the flight safety is compromised.. It does not mean that landing with a 757 at 105 tons is free of consequences for your plane.. It will just land without leaving the wings at the impact point, but believe me that it will have a huge impact on maintenance cost... In this case yes, you will be reading the DFDR data, looking at the acceleration, attitude, speed, weight at the impact, and after computing the stress, you will have to come with a specific maintenance program, that can involve gear, flaps, panels replacement, and even frames..

So in a few words, you have to demonstrate that your aircraft will hold, but believe me if you run an airline, you do not want your pilots to do that unless once again flight safety is compromised...

[Dmmoore]

That's not quite what the FAR reads, is it, Don? Nor is the term "no damage" found anywhere therein, is it? And if you can hold 6FPM at landing, you're a better pilot than I am, which I highly doubt. Better wrench, maybe, but better pilot, not likely.

Agreed. I should have reported it as FPS.

About 15 - 20 years ago I'd loved to have taken you into some of my Alaskan fishing holes. Those days are long gone for me. They won't issue a medical well, actually I didn't bother to ask. I'm not about to fly as PIC :shakehea: anymore. There was a time though when I'd match my piloting skills against anyone, well maybe not ITS :lol: in most single land or sea planes and the Widgeon, goose, or twin CeeBee.

[flyboy2548m]

About 15 - 20 years ago I'd loved to have taken you into some of my Alaskan fishing holes. Those days are long gone for me. They won't issue a medical well, actually I didn't bother to ask. I'm not about to fly as PIC :shakehea: anymore. There was a time though when I'd match my piloting skills against anyone, well maybe not ITS :lol: in most single land or sea planes and the Widgeon, goose, or twin CeeBee.

That was then and this....

[Gabriel]

No, it doesn't. There are plenty of qualifiers there. Refer to 25.723, .473 and .479.
I did

§ 25.473 Landing load conditions and assumptions.

(a) For the landing conditions specified in §25.479 to §25.485 the airplane is assumed to contact the ground—
(1) In the attitudes defined in §25.479 and §25.481;

(2) With a limit descent velocity of 10 fps at the design landing weight (the maximum weight for landing conditions at maximum descent velocity); and

(3) With a limit descent velocity of 6 fps at the design take-off weight (the maximum weight for landing conditions at a reduced descent velocity).

(4) The prescribed descent velocities may be modified if it is shown that the airplane has design features that make it impossible to develop these velocities.
25.479 refers to "the conditions prescribed in §25.473".

25.723 I don't care because it doesn't state a requirement for the airplane itself but a requirement for the tests used to validate "the analytical representation of the landing gear dynamic characteristics that is used in determining the landing loads", as 25.723 states itself.

However it goes on saying that "a range of tests must be conducted to ensure that the analytical representation is valid for the design conditions specified in §25.473" (and we know what 25.473 says), and also that the configurations for this tests "must include at least the design landing weight or the design takeoff weight, whichever produces the greater value of landing impact energy".
Nor is the term "no damage" found anywhere therein, is it?
Correct, the term "no damage" is not found anywhere in relation to a landing at MTOW, but then it is not found in relation to a landing at MLW either. In short, the airplane doesn't need to leave a 10 fps landing at MLW in any better shape than a 6 fps landing at MTOW.

However, the title of 25.473 is "Landing loads conditions and assumptions", and 25.473 is under FAR 25 subpart C: "Structure", which starts with:

Subpart C—Structure

General

§ 25.301 Loads.

(a) Strength requirements are specified in terms of limit loads (the maximum loads to be expected in service) and ultimate loads (limit loads multiplied by prescribed factors of safety). Unless otherwise provided, prescribed loads are limit loads.
Ok, it doesn't say that the airplane must be undamaged after encountering the loads expected in service. Some (I for example) might argue that that's implicit.

[flyboy2548m]

IOk, it doesn't say that the airplane must be undamaged after encountering the loads expected in service. Some (I for example) might argue that that's implicit.

You can argue anything you want, Gabriel, even that the sky is brown.

[Dmmoore]

"No damage" is implied. Otherwise a method of determining the amount of acceptable damage would have to be specified.

The Flight manual spells out overweight landing limits / restrictions. The 747-200F allowed overweight landings with a touchdown rate of descent of 300 FPM or less.

[flyboy2548m]

"No damage" is implied. Otherwise a method of determining the amount of acceptable damage would have to be specified.



I don't know what the Feds did or didn't imply. What I do know (as do you, I suspect) is airliners get damaged under normal loads every day of the week. That's one of those neat little advantages of having practical experience vs abundant theoretical knowledge.

[Gabriel]

I don't know what the Feds did or didn't imply. What I do know (as do you, I suspect) is airliners get damaged under normal loads every day of the week. That's one of those neat little advantages of having practical experience vs abundant theoretical knowledge.
Zapata... Si no la gana, la empata!

Ok, then the same holds true for a landing within MLW.

Forget (and forgive me) about the damage. Let's say that, from a structural integrity point of view, everything that the FAR's require/allow for a landing at design landing weight & 10fps, they also require/allow for a landing at design take-off weight & 6fps.

My original post was in response to this:

Quote:
<TABLE cellSpacing=0 cellPadding=6 width="100%" border=0><TBODY><TR><TD class=alt2 style="BORDER-RIGHT: 1px inset; BORDER-TOP: 1px inset; BORDER-LEFT: 1px inset; BORDER-BOTTOM: 1px inset">Originally Posted by 767 Driver

If you land with a normal or lower than normal descent rate (300 fpm or less) you SHOULD not structurally damage the aircraft. When they certify transport category airplanes, they are certified to land up to their max structural takeoff weight.

</TD></TR></TBODY></TABLE>


That is not entirely true [...]

But 767 Driver was right and Kell Kong was wrong, and that's what I addresed.

Later Kell went on saying:
I think I remember saying it is up to the manufacturer...But sorry I should rather say it's depending if they can demonstrate that airplane can land with maxi takeoff weight without breaking out..

The mistake here is the if they can I highlighted.

The manufacturer MUST demonstrate that the airplane can land with maxi take-off weight without breaking out (albeit not as hard as with a maximum-landing-weight landing), regardless of the fuel jettison issue.

Just to make it clear, 10fps is 600fpm, and 6fps is 360fpm, so while none of them is an "incredibly smooth landing", one must be specially careful not to just drop the plane on the runway if above MLW.

And you still have a 50% margin to "just bend it out" before it "breaks out".

[AJ]

Also don't forget that MLW is often just the stroke of a pen. On our fleet of 747-438s the majority have a 295,000kg MLW. One CEO we had bought cheaper aircraft, so three of the -438s, identical in all structural aspects, have a MLW of 285,000kg. If you land one of the cheaper jets at 292,000kg you have busted a limit, but the overweight landing inspection is very brief.

Same goes for our Boeing 767-336(ER)s. They have a MLW of 136,000kg compared to 145,100kg for all our -338(ER)s. If any urgency existed we would not hesitate in landing the -336 at 145,000kg as that 9,100kg would take 90 minutes to burn off!

[Kell Kong]

You guys can still try to decypher any authority note or recommendation... Good luck, just lawyer's talk.. But, what you forget is that the maintenace manual, ata chapter 05 is clear, overweight landing, unscheduled maintenance..

Talk all you can about what authorities say, but never land your aircraft above your MLGW, otherwise refer to ATA chapter 05 Maintenance manual..

Sorry to repeat that, but it's a no no...

[Gabriel]

You guys can still try to decypher any authority note or recommendation... Good luck, just lawyer's talk.. But, what you forget is that the maintenace manual, ata chapter 05 is clear, overweight landing, unscheduled maintenance..

Talk all you can about what authorities say, but never land your aircraft above your MLGW, otherwise refer to ATA chapter 05 Maintenance manual..

Sorry to repeat that, but it's a no no...
Kell, I'm no disputing that, but that an airplane WONT be damaged if it lands overweight and the landing is not too hard.

The manufacturer may then require all the maintenance hurdle that they see fit to verify that the landing was smooth enough (which is nothing incredible smooth) and if not to verify if there are damages and repair them if any.

That's why fuel will be dumped/burned whenever possible, but an overweight landing MUST be carried out in cases where time is critical (as a cabin fire). Lives have been lost several times while trying to achieve a MLW landing instead of landing ASAP. Now THAT's a no no.

The safety of the flight will not be compromised with an overweight landing, and the integrity of the airplane typically either (unless the landing is too hard). Maintenance and administrative hurdle after the safe overweight landing has been achieved is another issue.

So the ability to dump fuel is an operative advantage, and not as much a safety device, to avoid having a 747 that sucked a big bird at rotation circling for hours on three engines until it reaches the MLW or landing it overweight to avoid that with all the maintenance and administrative hurdle involved.

The decision for the manufacturer to include it or not in its design has nothing to do with the ability of a airplane to survive an overweight landing, as all airplane must be able to do it. I'm not sure but I think in some planes its even an option for the customer to order the airplane with or without the fuel jettison system.

That said, in certain exceptional cases, the dumping ability can make a difference from the safety point of view. The PanAm (?) 747 that lost a cargo door, and with it part of the side of the fuselage, some passengers and two engines on the same side, barely made it to the runway and it was dumping fuel all the way since the initial event to the landing. It still did land overweight IIRC, but the weight lost through dumping fuel might have made the difference between reaching the runway or landing short. I'm not sure why they had so much problem to keep altitude on 2 engines, since the 747 is able to do that at MTOW. Maybe the extra drag due to the big hole in the fuselage (there is no requirements in the FARs for an airplane to be able to keep flying with a big section o the fuselage missing).

[Dmmoore]

You guys can still try to decipher any authority note or recommendation... Good luck, just lawyer's talk.. But, what you forget is that the maintenance manual, ATA chapter 05 is clear, overweight landing, unscheduled maintenance..

Talk all you can about what authorities say, but never land your aircraft above your MLGW, otherwise refer to ATA chapter 05 Maintenance manual..

Sorry to repeat that, but it's a no no...

Correct.

In some cases the over weight landing inspection is divided into two parts. The 747 AMM allows for a Part 1 inspection for an over weight landing with a "Smooth" touch down and a Part 2 for over weight landings where the touch down was not smooth.

Part 1 took about an hour to accomplish. Part 1 required that part 2 be accomplished at the next scheduled letter check "B" or higher. Company procedure called for the DFDR to be pulled and sent to the main base for read out.

Part 2 took about 5 - 6 hours dwell time and a crew of 4 - 5 to accomplish.

Of the 3 over weight inspection I have been involved in, all were qualified as Part 1.

Whatever the AMM says.

[ptbodale]

Also don't forget that MLW is often just the stroke of a pen.
You are totally correct and the weights are changed to maximize load and to avoid airport fees. The 762's in AC fleet had a planned weight that was sufficient for continental North America, however once they were required for Hawaii or transAtlantic the weight was not sufficient so it was raised on a per flight basis. It was done on the approval of "Performance Engineering" and they would change the weights in the computer and we would assign and work the acft/flight.

[Dmmoore]

I feel the need to explain how and why some weights can be changed and some can not.

Boeing certifies the aircraft for specific maximum operating weights. Then (usually based on a customer request) Boeing will re-certify the aircraft for higher weights through the STC process. All conditions of the STC must be fully complied with before an aircraft can be certified to use the higher weights. One condition is payment. STC's are not free. The costs associated with obtaining an STC are passed along to the operator.

In some cases specific items must be modified or replaced to satisfy a condition. The Boeing 747-200F could be purchased with or without a sliding zero fuel weight option. Four of our aircraft were delivered from Boeing with the option. The other 6 did not have the option. However all structural modifications were accomplished during construction. All we needed to do in order to utilize the sliding zero fuel weight option was send Boeing a check for $50,000. Send Boeing a check, they send the STC and you can use the higher weights.

[Kell Kong]

In some cases specific items must be modified or replaced to satisfy a condition. The Boeing 747-200F could be purchased with or without a sliding zero fuel weight option. Four of our aircraft were delivered from Boeing with the option. The other 6 did not have the option. However all structural modifications were accomplished during construction. All we needed to do in order to utilize the sliding zero fuel weight option was send Boeing a check for $50,000. Send Boeing a check, they send the STC and you can use the higher weights.

That is the way it works, it is just a matter of certification.. Often MODs are expensive for just a Flight manual updating, or engine EEC pin programming for thrust increase for instance... But manufacturer consider that if you increase your payload, you will increase your income, so they want their part of the business too.. Fair enough.

And Don, I have seen a 3 months grounded 747 of Air France (F-GCBA if I recall well). Captain told aircraft did not flare, I guess they did a 3 points landing... was not nice to see. It ended with frames and skin replacement, for the most important job... Flaps, gears, etc as well... Expensive landing, in this case not overweight, but the result is the same.

[Gabriel]

And Don, I have seen a 3 months grounded 747 of Air France (F-GCBA if I recall well). Captain told aircraft did not flare, I guess they did a 3 points landing... was not nice to see. It ended with frames and skin replacement, for the most important job... Flaps, gears, etc as well... Expensive landing, in this case not overweight, but the result is the same.
What is the same than what?

[Kell Kong]

What is the same than what?

Overweight/hard landing falls under the same inspection tasks.. And result is the same...risk of high aircraft damage..

[Gabriel]

Overweight/hard landing falls under the same inspection tasks.. And result is the same...risk of high aircraft damage..

The risk of high aircraft damage is the hard landing, not the overweight. But yes, the probability of a landing of a given "hardness" to damage the plane increases with weight, meaning that a landing hard enough to damage the airplane if overweight might not damage it if not overweight. However, this is not a simple "overweight / not overweight" issue. I'm sure you'll agree that, for all structural integrity purposes, a 747 landing 500lb overweight is the same than the same 747 landing 500lb below MLW, even when the former will trigger maintenance work.

I don't know what is your experience with overweight landings (mine is zero). But Don mentioned that out of 3 overweight landings he faced, all 3 were done in must one hour of maintenance.

On the other hand, you mentioned the 3 months grounding of that 747 for a hard non-overweight landing. And that's nothing compared to what Iberia is facing with his A340 hard non-overweight landing at Quito.

I have only some theoretical knowledge about shock-absorbers dynamics, but at least in theory, as long as there is enough stoke, the major force while absorbing the energy of the impact (touchdown) will happen in the first instant, when the vertical speed is about to start to damp out. That's because the damping force is proportional to the speed of the strut compression, regardless of the weight. Of course, the highest the weight, the highest the mass, so the same force applied in the struts will produce a higher acceleration in a lightly loaded airplane than in a heavily loaded one. Passengers, and the rest of the airplane's structure, will feel a harder landing when the airplane is light that when the airplane is heavy (for the same vertical speed at touchdown). That also means that the lighter plane will slow down its vertical motion faster, and hence not compress the struts so much. In certain conditions (for example if the strut runs out of stroke) that could impose harder loads during the last instants of the compression, but I wouldn't be surprised if (in fact, I expect that) the 10fps landing at MLW is the limiting design criteria over the 6fps MTOW landing, specially since the difference between MTOW and MLW is never that much (relatively speaking, it could be thousands of pounds but in how many pounds of gross weight?)

Again, I have no real-life experience, but it looks to me that the two main differences between an overweight landing and a non-overweight one are:

- By default, a non-overweight landing is considered not hard unless the pilot reports it, while the overweight landing is considered hard until proven otherwise. That triggers maintenance tasks if at least to prove that the landing was not hard (1 hour job).

- An overweight landing is considered hard at some vertical speeds where a non-overweight landing is not considered hard yet. However, in both cases, if the landing is not hard you have no / minimal maintenance involved, while if the landing is hard there can be a lot of maintenance job, grounding time, and other costs, even the write-off of the airplane, overweight or not (again, ask Iberia).

So yes, land below MLW whenever possible, but if postponing the landing can endanger the flight, just land and forget about the weight. In any case (but especially if overweight) try not to land too hard.

[Dmmoore]

Gabriel,
For all practical purposes you are correct with this one addition. Any mechanic or flight crew member can call for a hard landing inspection "IF" damage typical of an over weight / hard landing were noticed during a walk around or preflight inspection.

A phase one inspection is only appropriate "IF" no damage is noted. Once damage is discovered, phase two must be accomplished.

[Kell Kong]

The risk of high aircraft damage is the hard landing, not the overweight. But yes, the probability of a landing of a given "hardness" to damage the plane increases with weight, meaning that a landing hard enough to damage the airplane if overweight might not damage it if not overweight. However, this is not a simple "overweight / not overweight" issue. I'm sure you'll agree that, for all structural integrity purposes, a 747 landing 500lb overweight is the same than the same 747 landing 500lb below MLW, even when the former will trigger maintenance work.

I don't know what is your experience with overweight landings (mine is zero). But Don mentioned that out of 3 overweight landings he faced, all 3 were done in must one hour of maintenance.

On the other hand, you mentioned the 3 months grounding of that 747 for a hard non-overweight landing. And that's nothing compared to what Iberia is facing with his A340 hard non-overweight landing at Quito.

I have only some theoretical knowledge about shock-absorbers dynamics, but at least in theory, as long as there is enough stoke, the major force while absorbing the energy of the impact (touchdown) will happen in the first instant, when the vertical speed is about to start to damp out. That's because the damping force is proportional to the speed of the strut compression, regardless of the weight. Of course, the highest the weight, the highest the mass, so the same force applied in the struts will produce a higher acceleration in a lightly loaded airplane than in a heavily loaded one. Passengers, and the rest of the airplane's structure, will feel a harder landing when the airplane is light that when the airplane is heavy (for the same vertical speed at touchdown). That also means that the lighter plane will slow down its vertical motion faster, and hence not compress the struts so much. In certain conditions (for example if the strut runs out of stroke) that could impose harder loads during the last instants of the compression, but I wouldn't be surprised if (in fact, I expect that) the 10fps landing at MLW is the limiting design criteria over the 6fps MTOW landing, specially since the difference between MTOW and MLW is never that much (relatively speaking, it could be thousands of pounds but in how many pounds of gross weight?)

Again, I have no real-life experience, but it looks to me that the two main differences between an overweight landing and a non-overweight one are:

- By default, a non-overweight landing is considered not hard unless the pilot reports it, while the overweight landing is considered hard until proven otherwise. That triggers maintenance tasks if at least to prove that the landing was not hard (1 hour job).

- An overweight landing is considered hard at some vertical speeds where a non-overweight landing is not considered hard yet. However, in both cases, if the landing is not hard you have no / minimal maintenance involved, while if the landing is hard there can be a lot of maintenance job, grounding time, and other costs, even the write-off of the airplane, overweight or not (again, ask Iberia).

So yes, land below MLW whenever possible, but if postponing the landing can endanger the flight, just land and forget about the weight. In any case (but especially if overweight) try not to land too hard.

Honestly, I am a bit tired of always being contradicted by you Gabriel, the point is, landing your aircraft when above maxi landing weight is not to be performed unless there is an emergency situation. I did not invent that rule.

Overweight/hard landing go through the same inspection task, starting by reading vertical acceleration at impact, then you will be instructed by the only reference manual (maintenance manual) what to do... I did not write the manual.

You can turn it the way you want, read it in chinese or in russian, in korean or in martian either, you will not escape this...

I think that I have made my point since a few days now. Sincerely, if this isn't of your liking, why don't you fill in a complaint to the manufacturers??

[flyboy2548m]

Honestly, I am a bit tired of always being contradicted by you Gabriel...

Now-now, Kell, that's like being mad at a dog just for being a dog, not even for barking.

[Gabriel]

Gabriel, the point is, landing your aircraft when above maxi landing weight is not to be performed unless there is an emergency situation. I did not invent that rule.

Overweight/hard landing go through the same inspection task, starting by reading vertical acceleration at impact, then you will be instructed by the only reference manual (maintenance manual) what to do... I did not write the manual.

I think that I have made my point since a few days now. Sincerely, if this isn't of your liking, why don't you fill in a complaint to the manufacturers??
No, no. This last post is of my liking and I agree 100% with it.

I'll let the forummates judge if it is consistent with your or my previous posts.

[peter b. aden]

Here is Boeing's list on which of their commercial aircraft have fuel dumping capabilities . Enjoy http://www.boeing.com/commercial/airports/faqs/fueldump.pdf

You all have a great flying day
Peter