Last Minute Changes
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Last Minute Changes
Hi Guys quick question im compiling a list of companies with their max LMC if exceeded then a new load sheet must be provided (preference to a320 operators)...... thks for any responses 
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To the A320 , 500 Kgs.
To the A-330 , 1000Kgs.
Note that LMC doesn`t include fuel . If you need to fuel up or defuel another loadsheet has to be done.
Cheers
To the A-330 , 1000Kgs.
Note that LMC doesn`t include fuel . If you need to fuel up or defuel another loadsheet has to be done.
Cheers
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JT
It's not a pointless question really with many loadsheets now being simplified due to computer based W&B.
It depends on what the allowable LMC limit is before a new W&B is required. In our case (A319) changes up to 500kg, with certain other restrictions in individual holds, may signed off without recalculating Balance. Just a quick weight adjustment calc and go. Outside those limits it's a full W&B.
The actual design of the loadsheet means nothing other than how much space their is to record the LMC.
It's not a pointless question really with many loadsheets now being simplified due to computer based W&B.
It depends on what the allowable LMC limit is before a new W&B is required. In our case (A319) changes up to 500kg, with certain other restrictions in individual holds, may signed off without recalculating Balance. Just a quick weight adjustment calc and go. Outside those limits it's a full W&B.
The actual design of the loadsheet means nothing other than how much space their is to record the LMC.
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Sorry ... the trimsheet design is critical ... the LMC situation depends on what has gone into the error analysis and how much the limits are constrained in association.
A computer calculation has the advantage of being able to do the exercise more accurately etc., but, if the trimsheet is designed by a moderately competent weight control person (nothing difficult in the design .. it just takes a bit of care and good housekeeping), and executed with a modicum of diligence (by the user), the trimsheet CG will be as good functionally as the computer's answer.
Point is, if you dumb down the trimsheet too much, there is no point in having one in the first place .. the only use for a trimsheet is to be able to arrive at an accurate answer a lot quicker than some other way .. otherwise you would use the other way according to your preferences.
Perhaps I should have said something along the lines of "it is pointless comparing LMC figures for different trimsheets or for different Types ?"
It depends on what the allowable LMC limit is before a new W&B is required ..
... means error analysis and limit constraints which went into the design of the sheet ... YOUR 500 kg just happens to be the number for YOUR trimsheet .. now, if one did the job differently (for the same Type) .. the number might easily be 200 kg, or 329 kg .. or whatever.
The only caveat is that an operator could easily adopt a "standard" LMC delta for LMCs across all Types in the operation for standardisation .. but that is not really relevant to your question.
There is just no "one size fits all".
A lot depends on the needs of the operator and load control organisation and, in many instances, the preferences of the sheet designer.
FWIW I've designed somewhere around two hundred trimsheets over the past 35 years or so ... (guess that just means I've just made a lot more mistakes than have most other trimsheet designers ...)
A computer calculation has the advantage of being able to do the exercise more accurately etc., but, if the trimsheet is designed by a moderately competent weight control person (nothing difficult in the design .. it just takes a bit of care and good housekeeping), and executed with a modicum of diligence (by the user), the trimsheet CG will be as good functionally as the computer's answer.
Point is, if you dumb down the trimsheet too much, there is no point in having one in the first place .. the only use for a trimsheet is to be able to arrive at an accurate answer a lot quicker than some other way .. otherwise you would use the other way according to your preferences.
Perhaps I should have said something along the lines of "it is pointless comparing LMC figures for different trimsheets or for different Types ?"
It depends on what the allowable LMC limit is before a new W&B is required ..
... means error analysis and limit constraints which went into the design of the sheet ... YOUR 500 kg just happens to be the number for YOUR trimsheet .. now, if one did the job differently (for the same Type) .. the number might easily be 200 kg, or 329 kg .. or whatever.
The only caveat is that an operator could easily adopt a "standard" LMC delta for LMCs across all Types in the operation for standardisation .. but that is not really relevant to your question.
There is just no "one size fits all".
A lot depends on the needs of the operator and load control organisation and, in many instances, the preferences of the sheet designer.
FWIW I've designed somewhere around two hundred trimsheets over the past 35 years or so ... (guess that just means I've just made a lot more mistakes than have most other trimsheet designers ...)
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In so many airlines now it's computerised (in my company's case, laptop/toughbook) anyway so there is no noticeable trimsheest design as such.
That's exactly why operators can say effectively 'bung in the numbers, check them, and look at the result'.
The original question I believe referred to exactly what many guys have answered. Having done the first bit as described above the trim part does not need to be recalculated until a certain limit is reached (either total or in an individual hold) because that falls in with the error factor allowed.
I don't see anyone here suggesting that it should be the same for everyone or every type - now that would be nonsense!
That's exactly why operators can say effectively 'bung in the numbers, check them, and look at the result'.
The original question I believe referred to exactly what many guys have answered. Having done the first bit as described above the trim part does not need to be recalculated until a certain limit is reached (either total or in an individual hold) because that falls in with the error factor allowed.
I don't see anyone here suggesting that it should be the same for everyone or every type - now that would be nonsense!
Moderator
You miss the point of the discussion, my friend.
The computer analysis runs the same way as the paper trimsheet if we are dealing with LMCs (ie no data re-entry). The LMC quantum is entirely arbitrary and there is no validity in comparing this aircraft/operator with another ... other than in the vein of "my LMC is bigger than yours .."
If you choose to view the matter differently, then that is fine .. but it doesn't make your view any less incorrect from a technical engineering perspective ...
The computer analysis runs the same way as the paper trimsheet if we are dealing with LMCs (ie no data re-entry). The LMC quantum is entirely arbitrary and there is no validity in comparing this aircraft/operator with another ... other than in the vein of "my LMC is bigger than yours .."
If you choose to view the matter differently, then that is fine .. but it doesn't make your view any less incorrect from a technical engineering perspective ...
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I haven't missed the point of the discussion at all. You have simply decided that the original question was not worth asking. No-one surely cares who has the bigger LMC, just interest as to why they might be different.
Maybe he/she was just interested in knowing the numbers!
The figures used by my company are not arbitrary. They have been researched by the Perf dept and given as a total OR fwd/aft hold limits that keep the trim within limits accepted by the authority as not requiring a recalculation; ie. at the limits of LMC in any area, the effect on trim will not have a significant performance effect.
As every take off is based on improved climb and a small weight change can produce a relatively significant flex/v speed change, the take off figures are always recalculated.
If others have different limits for different aircraft - fine. If the authority is OK with, carry on.
I still maintain the original question cams across as being asked out of curiosity - hence the answers that followed.
Maybe he/she was just interested in knowing the numbers!
The figures used by my company are not arbitrary. They have been researched by the Perf dept and given as a total OR fwd/aft hold limits that keep the trim within limits accepted by the authority as not requiring a recalculation; ie. at the limits of LMC in any area, the effect on trim will not have a significant performance effect.
As every take off is based on improved climb and a small weight change can produce a relatively significant flex/v speed change, the take off figures are always recalculated.
If others have different limits for different aircraft - fine. If the authority is OK with, carry on.
I still maintain the original question cams across as being asked out of curiosity - hence the answers that followed.
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733/735
No mass or passenger limit, however if the index change is greater than +-6 index units the balance chart has to be redone, more than 500kg change results in recalculation of actual takeoff- zerofuel- and landing mass as well as recalculation of corresponding performance data and speeds.
Last minute changes of fuel is limited to 500kg.
No mass or passenger limit, however if the index change is greater than +-6 index units the balance chart has to be redone, more than 500kg change results in recalculation of actual takeoff- zerofuel- and landing mass as well as recalculation of corresponding performance data and speeds.
Last minute changes of fuel is limited to 500kg.
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FlaspOne,
Apologies if I appeared to be argumentative .. for that was not my intention. Perhaps my original comment could have been couched in gentler terms ?
However, having spent a lifetime in engineering (including a lot of weight control) and airline flying (where I could see the front end problems caused by unhelpful loading systems), the general level of misunderstanding in the pilot ranks has always caused me some concern.
Unfortunately, the typical pilot training for weight control rarely extends beyond how to complete the loading system .... in general the detailed knowledge in the pilot ranks of how it all works tends to be limited and, in my view, it is a desirable aim to improve that level of knowledge.
the original question was not worth asking
.. not what I said ... the question is well worth asking if the end result is a bit more knowledge. However, it is "pointless" in that the LMC numbers are quite arbitrary and direct comparison between one loading system and another is of little value. Quite different considerations.
Maybe he/she was just interested in knowing the numbers
If so, then fine.
just interest as to why they might be different.
Ah .. it appears that we are on the same path, my friend ... so let the discussion continue
The figures used by my company are not arbitrary
Perhaps we are at loggerheads because of semantics. By "arbitrary", I mean that the LMC number chosen is so chosen as the result of whatever considerations went into the particular loading system .. ie, there is nothing at all sacrosanct in the particular number which ends up in your sheet .. for the same aircraft, one can readily generate a number of different loading systems each with a different LMC number or, indeed, several numbers .. this makes the sheet a little more complex but is useful on occasion.
It is just a matter of matching the number desired to fit the convenience of the loading system against the manner in which the error analysis and drafting of the trimsheet is done.
They have been researched by the Perf dept
Precisely my point .. the performance department operations engineers (which is my principal background) traditionally have responsibility for weight control matters. As part of the design of the loading system, those good folk have determined what figure is suitable for the particular operation .. and then arranged the design of the sheet to suit that figure. However, it is important to realise that they could just as easily have determined that a different delta was to be the LMC figure ..
the effect on trim will not have a significant performance effect
At the risk of inflaming the discussion, your view here is misplaced. The LMC, per se, has naught to do with performance in general. Rather the LMC defines, within the error analysis for the trimsheet, the maximum calculation misloading (in that the load now differs from the calculation) which will not cause the actual CG to be outside the certification CG envelope .. no more, no less.
the take off figures are always recalculated
Absolutely .. however LMC, while usually couched in terms of weight deltas, has little to do with weight as such and everything to do with IU (as an indirect measure of CG).
if the index change is greater than +-6 index units
Denti is onto the thrust of LMCs .. we are concerned with the net effect of a misload on the CG.
If the trimsheet is well designed (which, in general, includes choosing a datum which gives a reasonably boxy envelope shape) then it may be practicable to give the LMC in simple IU delta terms. In the more general case, the designer looks at the plotted effect of a specific weight change .. if effect, one chooses the desired LMC weight delta and then redraws the envelope limit so that this level of misload constrains the actual CG (as opposed to the calculated CG) to remain within the envelope limits.
FlapsOne .. please don't think I have any interest in being contrary for the sake of it .. there is a useful purpose to be served by continuing this discussion for others. Please do respond with specific questions and I am only too happy to address them ..
You might also consider sitting down with one of your ops engineers and having him/her run you through how they designed your particular trimsheet .. I would be VERY surprised if the story differs from mine in any material regard ...
Apologies if I appeared to be argumentative .. for that was not my intention. Perhaps my original comment could have been couched in gentler terms ?
However, having spent a lifetime in engineering (including a lot of weight control) and airline flying (where I could see the front end problems caused by unhelpful loading systems), the general level of misunderstanding in the pilot ranks has always caused me some concern.
Unfortunately, the typical pilot training for weight control rarely extends beyond how to complete the loading system .... in general the detailed knowledge in the pilot ranks of how it all works tends to be limited and, in my view, it is a desirable aim to improve that level of knowledge.
the original question was not worth asking
.. not what I said ... the question is well worth asking if the end result is a bit more knowledge. However, it is "pointless" in that the LMC numbers are quite arbitrary and direct comparison between one loading system and another is of little value. Quite different considerations.
Maybe he/she was just interested in knowing the numbers
If so, then fine.
just interest as to why they might be different.
Ah .. it appears that we are on the same path, my friend ... so let the discussion continue
The figures used by my company are not arbitrary
Perhaps we are at loggerheads because of semantics. By "arbitrary", I mean that the LMC number chosen is so chosen as the result of whatever considerations went into the particular loading system .. ie, there is nothing at all sacrosanct in the particular number which ends up in your sheet .. for the same aircraft, one can readily generate a number of different loading systems each with a different LMC number or, indeed, several numbers .. this makes the sheet a little more complex but is useful on occasion.
It is just a matter of matching the number desired to fit the convenience of the loading system against the manner in which the error analysis and drafting of the trimsheet is done.
They have been researched by the Perf dept
Precisely my point .. the performance department operations engineers (which is my principal background) traditionally have responsibility for weight control matters. As part of the design of the loading system, those good folk have determined what figure is suitable for the particular operation .. and then arranged the design of the sheet to suit that figure. However, it is important to realise that they could just as easily have determined that a different delta was to be the LMC figure ..
the effect on trim will not have a significant performance effect
At the risk of inflaming the discussion, your view here is misplaced. The LMC, per se, has naught to do with performance in general. Rather the LMC defines, within the error analysis for the trimsheet, the maximum calculation misloading (in that the load now differs from the calculation) which will not cause the actual CG to be outside the certification CG envelope .. no more, no less.
the take off figures are always recalculated
Absolutely .. however LMC, while usually couched in terms of weight deltas, has little to do with weight as such and everything to do with IU (as an indirect measure of CG).
if the index change is greater than +-6 index units
Denti is onto the thrust of LMCs .. we are concerned with the net effect of a misload on the CG.
If the trimsheet is well designed (which, in general, includes choosing a datum which gives a reasonably boxy envelope shape) then it may be practicable to give the LMC in simple IU delta terms. In the more general case, the designer looks at the plotted effect of a specific weight change .. if effect, one chooses the desired LMC weight delta and then redraws the envelope limit so that this level of misload constrains the actual CG (as opposed to the calculated CG) to remain within the envelope limits.
FlapsOne .. please don't think I have any interest in being contrary for the sake of it .. there is a useful purpose to be served by continuing this discussion for others. Please do respond with specific questions and I am only too happy to address them ..
You might also consider sitting down with one of your ops engineers and having him/her run you through how they designed your particular trimsheet .. I would be VERY surprised if the story differs from mine in any material regard ...
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There are several aspects to a potential LMC.
Weight can go up or down or the CG can move either way depending on what's done.
If the weight goes up with 4 extra pax and bags on a hot in day in Malaga pointing at the mountains for take off then it has everything to do with weight and how much poke is coming out of my engines - especially if one fails.
Weight can go up or down or the CG can move either way depending on what's done.
Absolutely .. however LMC, while usually couched in terms of weight deltas, has little to do with weight as such and everything to do with IU (as an indirect measure of CG).
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L1011.
In flying the aeroplane for 27 years, I have found that it is nearly impossible to mis-load the aircraft, due to the unique design of the machine.
That rather large all-flying horizontal stab is the key.
Set 4 units nose up, and it works every time, heavy or light.
Having said this, at the present airline, last minute changes are handled with a new loadsheet...but the Flight Engineer, who does the deed, seems to complain quite a lot....
Having said this, we don't seem to have many last minute changes...the aeroplane is full all the time.
Surprise, surprise.
In flying the aeroplane for 27 years, I have found that it is nearly impossible to mis-load the aircraft, due to the unique design of the machine.
That rather large all-flying horizontal stab is the key.
Set 4 units nose up, and it works every time, heavy or light.
Having said this, at the present airline, last minute changes are handled with a new loadsheet...but the Flight Engineer, who does the deed, seems to complain quite a lot....
Having said this, we don't seem to have many last minute changes...the aeroplane is full all the time.
Surprise, surprise.
