# A320 CG correction when to apply?

Thread Starter

Join Date: Mar 2009

Location: FL370

Posts: 100

**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%.

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%.

Join Date: Jan 2007

Location: seoul Korea

Age: 49

Posts: 31

The note confuses me too; the second note says

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.

**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.*

Join Date: Jan 2007

Location: seoul Korea

Age: 49

Posts: 31

Only half a speed-brake

Join Date: Apr 2003

Location: Commuting home

Age: 42

Posts: 3,024

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.

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.

Join Date: Oct 2007

Location: World

Posts: 486

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.

Let's check PER-TOF-TOC-10-20 TAKE OFF CHART DESCRIPTION , Corrections due to Different Take Off Conditions and check the "note" field.

Join Date: Jan 2004

Location: Here and there

Posts: 2,853

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.

Only half a speed-brake

Join Date: Apr 2003

Location: Commuting home

Age: 42

Posts: 3,024

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.

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.

Join Date: Mar 2012

Location: Having a margarita on the beach

Age: 48

Posts: 1,762

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%.

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 %.