View Full Version : cost index for lrc in A320

23rd Jul 2011, 05:44
Hi,just getting a little confused.The A320QRH,in flt performance page 4.11 states that for quick determination of CILRC use 25ci for kgs/min.I would refer to in flt performance LRC in vol3 to extract my speeds in case of a diversion.However there are a lot of pilots insisting that ci0 would give us LRC speeds and some who mention ci15 for diversions at LRC.I understand that the fuel pred fmgs predictions are based on ci0 and fixed levels [220 and 310[depending on the dist to go.So whats the strategy to be followed in case of a diversion at Lrc.And which ci gives us LRC.

23rd Jul 2011, 10:13
Hi ssflying,

This link to Getting_To_Grips_With_The_Cost_Index (http://www.smartcockpit.com/data/pdfs/flightops/aerodynamics/Getting_To_Grips_With_The_Cost_Index.pdf) should keep you occupied for a while.
I'd say minimum fuel = Cost index 0.

The leg distance to your Alternate may be so short that you would hardly notice the difference with CI 0, 15 or 25 inserted, so I would use a sensible index which predicted I'd arrive with sufficient fuel.

23rd Jul 2011, 12:41
CI zero is for MAXIMUM RANGE

In your model, if you insert CI 25 you will have, approximately, LRC mach number.

Notice that in most airlines current CI is lower than LRC, so if you want to fly at LRC you have to accelerate.

capt. solipsist
23rd Jul 2011, 13:05
(old QRH 4.11):

For a quick determination of the CILRC, use:

CILRC = 40 kg/min

which means, 2400 kg/hr, which means 1200 kg/hr PER engine.

Funny thing is, it works out around CI 40 on typical weights :ok:

23rd Jul 2011, 17:18
Do not confuse CI kg/min with FF Kg/min, which is a very common thing.

a 40 Kg/min CI means that for the airline one minute of flight is worth as much as 40 kg of fuel. Therefore, cruise speed will be increased from max range speed until one minute of time saved costs more than 40 kg of extra burnt fuel. When that occurs you are flying at the ECON MACH.

In the 320 this is often difficult to see, since we can only see whole minutes and hundreds of kgs of fuel.

capt. solipsist
24th Jul 2011, 02:50
Finally found the other reference for Cost Index Long Range Cruise:

FCOM 4.05.50 p14 :ok:

(I am not confused, after all :})

Last Ditch
25th Jul 2011, 08:27
This is waste of one page in QRH. And, a few bytes in my brain.
If fuel is a concern, set CI=0.
If fuel is not a concern, set CI as specified by your company.
If you want to fly for endurance, fly green dot (plus a few knots if you anticipate turns).

25th Jul 2011, 13:27
Capt solpstic

CI Kg/min is not a measure of FF. It is a measure of time value in terms of fuel. That's what I meant with "confusion".