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A320 CG correction when to apply?

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A320 CG correction when to apply?

Old 14th Dec 2015, 13:25
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Cool A320 CG correction when to apply?

Dear fellow pilots,I was wondering when to apply CG correction during takeoff speed calculation concerning (increasing v speeds by 1 kt and decreasing flex by 2 degrees) is it when below 25% or 27% because the FCOM states the following which is confusingplease state the answer for both RTOW and LPC)
PER-TOF-TOC-14-10 P 1/10

CORRECTIONS DUE TO DIFFERENT TAKEOFF CONDITIONS
when the takeoff conditions are different from those provided on the chart,apply associated corrections.
Note: -if the RTOW chart is based on the CG being at 25%,the crew can determine the flexible temperature at a more forward CG by decreasing flexible temperature by 2 degrees.V speeds must be increased by 1 kt.
-25% is the basic certified limit,on which all takeoff computations are based.To take into account the operational margins,the above penalties must be applied when operational CG is forward 27%.
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Old 14th Dec 2015, 17:38
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Forward of 27%
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Old 30th Sep 2016, 06:01
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The note confuses me too; the second note says 25% is the basic certified limit, on which all takeoff computations are based. As the aforementinoed note says, if the computations are already based on 25%, why does the FCOM tell us to apply panelties when CG is forward of 27%? After all, 25% is worse than 27% in terms of performance isn't it?
Maybe, just maybe, FCOM dose not mean that RTOW chart for A320 is based on 25%; I am wondering what CG position does the RTOW chart use for calculations.

Last edited by simyoke; 30th Sep 2016 at 06:49.
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Old 30th Sep 2016, 12:22
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seems clear to me that you apply it if it is forward or 27% in order to maintain a margin, I.e, they don't want to be right on the 25% limit.
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Old 30th Sep 2016, 14:28
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Originally Posted by AerocatS2A View Post
seems clear to me that you apply it if it is forward or 27% in order to maintain a margin, I.e, they don't want to be right on the 25% limit.
The muddling point is that if RTOW chart computations are done with 25% CG why bother with 27%? 25 is more forward than 27%.
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Old 30th Sep 2016, 14:56
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Plug the numbers into the iPad and let it do its magic... Is there more to it?
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Old 30th Sep 2016, 20:34
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Denti, depends on how your iPad (or whatever app you're using) is configured. The label is modifiable by the administrator, ours currently reads <= 27%.

Answer: according to Airbus guidance, the limit when to apply alternative forward CG lo-speed performance corrections is 27% indicated CG. (reference available).

The logic is, as I understand it: The aircraft is flown-certified with 25% CG position as the differentiating value. In controlled condtions, loading-wise, that is.

Because in real life operating scenario, the calculated / indicated CG postion is only approximation of actual CG - true passanger weight distribution being the most variable factor - a conservative margin of 2% is normally added to the limiting value.

It is easy to understand that RTOW charts show 25% because that's how they are calculated, but to use them without a correction for forward CG, one needs LDS figure of 27 or more.
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Old 1st Oct 2016, 01:50
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Originally Posted by FlightDetent View Post
Denti, depends on how your iPad (or whatever app you're using) is configured. The label is modifiable by the administrator, ours currently reads <= 27%.

Answer: according to Airbus guidance, the limit when to apply alternative forward CG lo-speed performance corrections is 27% indicated CG. (reference available).

The logic is, as I understand it: The aircraft is flown-certified with 25% CG position as the differentiating value. In controlled condtions, loading-wise, that is.

Because in real life operating scenario, the calculated / indicated CG postion is only approximation of actual CG - true passanger weight distribution being the most variable factor - a conservative margin of 2% is normally added to the limiting value.

It is easy to understand that RTOW charts show 25% because that's how they are calculated, but to use them without a correction for forward CG, one needs LDS figure of 27 or more.
Correct. Sometimes reading the notes on the FCOM is worth the time.
Let's check PER-TOF-TOC-10-20 TAKE OFF CHART DESCRIPTION , Corrections due to Different Take Off Conditions and check the "note" field.
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Old 1st Oct 2016, 05:30
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Originally Posted by simyoke View Post
The muddling point is that if RTOW chart computations are done with 25% CG why bother with 27%? 25 is more forward than 27%.
Correct, RTOWs are for a 25% CG. If the CG is forward of 25% then the RTOWs aren't valid. However the calculated CG is not 100% accurate, so to allow for a small amount of error, the CG adjustment is made if the calculated CG is 27% or less. They are being conservative.
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Old 1st Oct 2016, 09:38
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Thank you very much, Captain.
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Old 1st Oct 2016, 09:40
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Thanks much for the clarification. Really appreciate.
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Old 18th Oct 2020, 13:38
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Angel

what effect do these corrections have on the aircraft in practical terms though?
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Old 18th Oct 2020, 14:06
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In practical terms, once you accept "almost ok" in the flight preparation stage you'll eventually end up with a smoking hole later. Sets the wrong example for the cannon fodder.

Smartarsing aside, I think the controllability may not be the direct victim but climb gradient would be (larger control surfaces deflection) The FCOM corrections are +1 on speeds and -2 on FLEX, IIRC.
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Old 18th Oct 2020, 16:43
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Originally Posted by Flyman35 View Post
Dear fellow pilots,I was wondering when to apply CG correction during takeoff speed calculation concerning (increasing v speeds by 1 kt and decreasing flex by 2 degrees) is it when below 25% or 27% because the FCOM states the following which is confusingplease state the answer for both RTOW and LPC)
PER-TOF-TOC-14-10 P 1/10

CORRECTIONS DUE TO DIFFERENT TAKEOFF CONDITIONS
when the takeoff conditions are different from those provided on the chart,apply associated corrections.
Note: -if the RTOW chart is based on the CG being at 25%,the crew can determine the flexible temperature at a more forward CG by decreasing flexible temperature by 2 degrees.V speeds must be increased by 1 kt.
-25% is the basic certified limit,on which all takeoff computations are based.To take into account the operational margins,the above penalties must be applied when operational CG is forward 27%.
PER-LOD-WBA-LTS

Note:When referring to CG lower than 27 %, an operational margin is taken into account. It is the reason why performance at forward CG (lower than 25 %) must be used for operational CG lower than 27 %.

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Old 18th Oct 2020, 18:37
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@sonic: In practical terms, the OP probably goes under Flyman40 these days. You reckon?
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Old 19th Oct 2020, 08:09
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Originally Posted by FlightDetent View Post
@sonic: In practical terms, the OP probably goes under Flyman40 these days. You reckon?
Ahah yes I believe so !
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