A320 Cost Index
 

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!

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

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?

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.

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

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

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

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

.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.

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

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...

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