Airbus cost index and LRC
 

Can someone confirm that setting LRC in the A320 /321 requires reference to the LRC tables and manual setting of a specific Mach number that will vary as the weight decreases, rather than setting of a specific Cost Index.

I understand cost index 0 is max range and cost index 999 is min time but we never refer to LRC in our company documents except for some non normal ops.

The 2008 “Getting to grips with Cost Index” doesn’t appear to discuss LRC at all.

Thanks in advance.

Does this help? PRO-NOR-SRP-01-50 P 15/16

COST INDEX FOR LONG-RANGE CRUISE
The flight crew can use the table below to find an approximate Cost Index value that is calculated for cruise at long-range cruise speed. This value is valid for CRZ FL = OPT ALT ± 1 000 ft.

ENGINE / CILRC kg/min / CILRC 100 lb/h
CFM 56-5-A1/A3 45 60
CFM 56-5-A4/A5 40 55
CFM 56-5-B1/B2/B3 65 85
CFM 56-5-B4 (A321) 65 85
CFM 56-5-B4 (A320) 55 75
CFM 56-5-B4/P 25 35
CFM 56-5-B5/B6/B7 25 35
CFM 56-5-B5/2P CFM 56-5-B6/2P CFM 56-5-B7/2P 30 40
CFM 56-5-B8/B9 15 20
CFM LEAP-1A 40 55
PW6122/PW6124 20 30
PW1100G-JM 40 55
V2500-A1 45 60
V2522-A5/V2524-A5/ V2527M-A5 50 70
V2530-A5/V2533-A5 50 70
V2527-A5/V2527E-A5 40 55

You can also try out the numbers on Planestats https://www.planestats.com/bhsn_2018dec

Wow. There’s something else the archaic 737 does with just a button push........

Ive never understood this table even though I have seen it. Tthey're not saying, as far as I can understand, that we set a cost index 40 for LRC because from what I can see in my case using the IAE 2527 engines the value of 40 is representative of 40 kg/hour not a cost index of 40. I’m obviously missing something.

Seems like nobody else understands it either.

You can use a cost index, but it will depend on flight level and weight.
Airbus‘ document „Getting to grips with the cost index“, appendix 6, has some diagrams for LRC cost indices.

So I've looked at that graph but it still doesn't make sense to me (I'm looking at the version II 1998 appendix 6) it shows at the bottom of that graph that "Cost Index = KG per minute" and that we would potentially have 8 kg per minute burn for LRC which is clearly not correct aws that would only be 480 kgs per hour. Obviously I am missing something in the interpetation of this chart but I don't know what it is.

CI is price of kg of fuel devided by price of minute of flight. Setting CI 25 you say to an aircraft "Hay man, price of 1 minute is the same as price of 25 kg of fuel. Set such speed to save as mach money as you can". CI is not about fuel, it is about money.

I believe the QRH in the A320 specifies LRC CI as 40Kg/min. So we would adjust the cost index till we could see 40kg/min on the FUEL SD page.

No. CI have no direct connection with fuel burn. It is well discribed in GTG with cost index.

No.
What you see in the table is the approximate CI that equates to LRC.
The unit of CI being kg/hr (metric) or 100 lb/hr (imperial).
Agreed that adding the unit only leads to confusion.

https://cimg4.ibsrv.net/gimg/pprune....6cb95ba1d.jpeg
ref: GTG a/c perf

Ok so how do we set our selves up for LRC, not interested in what it costs?

Simple: just insert the CI of the LRC.

Most airlines fly a CI lower than the one associated to LRC, somewhere between LRC and MRC. LRC is actually a speed increase and range reduction in many cases.
Otherwise LRC continues to be a concept used in planning stage for driftdown, decompression, ETOPS/EDTO.

Ok and how do we know what cost index to insert for LRC?

scroll up. CI is given in PRO NOR SRP

Ok cool, our company’s A320’s have the VA2527-5A engines and from my understanding of that table, as long as we are 1000 feet +/- from the optimum level we can adjust and find an approximate cost index value for LRC which in turn will give us 40kg/min for this engine type, correct?

No. read my post again.
CI=40
The unit of CI is kg/min but this does not resemble a Fuel Flow!!

https://cimg4.ibsrv.net/gimg/pprune....99058791a9.png
Ok I get the fuel flow bit but how do we explain the cost index being 17 and not 40 as you have suggested given in this example using these graphs?

40 was just an example, a number you came up with.
Note that CI for LRC is to be extracted from FCOM/PRO/NOR/SRP/FMS/Prep for descent and approach