A320 Cost Index

[PT6A]

Hi,

Does anyone have any further information regarding the cost index on the A320 family?

I have read the FCOM and the Airbus getting to grips with cost index...

But specifically, a table of a given cost index vs the target mach number, and how much % wise the aircraft can "drift" from this target due to wind?

Just to further my own knowledge!

Thanks in advance!

[Microburst2002]

There are tables, "somewhere" in the fcoms, for various CIs and winds and weights.

[Slasher]

Question for you Micro while we're at it (if you don't mind) -

Changing CI from 18 to 0 in CRZ results in a slightly higher REC MAX but
can you tell me if the margin is reduced or not? I get the impression it is.

On the Prog page with 18 - 350 350 363 / with 0 - 350 355 369

Looked up the speeds in FCOM and I calculate from 363 to 369 the margin
reduces by 2 knots.

Assuming I'm correct - why would the buffer reduce for the same GW?

[Canuckbirdstrike]

The buffer is G related. It is 1.3g and it does not change with CI choices. To put perspective on this a 30 degree bank turn is 1.15G and light turbulence is 1.05 to 1.1G.

[Slasher]

It is 1.3g and it does not change with CI choices.

Well that's what I've always thought. Look up the speeds for 1G stalls clean.

[PT6A]

Got the data! I forgot the PEP had it in the enroute planning tab

[john_tullamarine]

Prefer not to close threads unless you have a specific reason to do so. Others may find the commentary useful.

[Microburst2002]

buffet limit is not CI related

The REC MAX gives a .2 g margin, I think.

I can't see why it changes with CI

[Slasher]

.2G buffer translated into a speed margin in the 1.0G case Micro.

I can't see why it would change with a reduction of CI either.

Never mind. I'm hardly ever up that high anyway.

[capt. solipsist]

REC MAX gives you .3G buffet margin, but you can choose a FL higher than that limited by .2G margin

[Stuck_in_an_ATR]

From the FCOM:

RECOMMENDED MAXIMUM ALTITUDE (REC MAX)

The recommended maximum altitude is the lowest of the maximum altitude that:

So, it's not only about buffet margin, but also performance-related. My guess is that with lower CI the a/c flies at lower speed, thus is able to maintain it (or climb) using less thrust - hence higher REC MAX FL...

[PT6A]

Do you want me to run some tables from the PEP for you guys? It shows everything in far more detail than the FCOM