21st Jul 2003, 02:40
Sorry if this has been covered in the past,
We have been operating a fixed CI for the last 6 or 7 years- it came about to give a sensible(280+ kts ) descent when fuel was enormously expensive. Obviously this was a bit daft considering the descent is only a minor portion of the flight. Finally things are starting to change,but I was looking for any info on how other airlines operate with regard to CI/econ (or not) and any useful links anyone might have,
I didnt make the rules,before anyone launches off- I can see its not the best idea in the world!
Thanks in advance
The operator I fly for uses a CI which "approximates LRC" - and is not an application of CI as such - at either end of the range COI "0" is used for min fuel and CI 300 for min time, with a "normal" CI 60/70 being used as the standard. If you think of CI as "LRC with brains" ie, varies with wind as well as weight, then we use it as a "smart" LRC speed generator - but I guess lots of performance engineering departments have their own ideas - I would be interesyted if any operators actually use CI as originally intended, ie, a consideration of total actual operating costs v fuel v time ?
22nd Jul 2003, 21:43
The fundamental rationale of the cost index concept is yo achieve minimum trip cost by means of trade-off between operating cost per hour and incremental fuel burn with time related cost , the faster the aircraft is flown the more is saved. THis is cos the faser you fly , the more milestime related components can be used and the more miles can be flown. However if the aircraft is flown faster to reduce time , fuelburn increases and mony will be lost in turn. The CI is used to take into account the relationship between fuel and time related cost. The FMS is able to counterbalance these cost factor in order to generate the min cost speed ( ECON)which takes into account only A/C and environmental factors. The CFP will select the min cost CI considering fuel,maintenance and overflying cost for given sector and a/c type. the overflying cost is included on routes where have more than one route selection is available. The CI value appears for CRZ as CI XXX, where XXX is cost index value.
For cross checking fuel figures, utilize FMS as primary tool or the flight planning and performance manual.The cost index for LRC would be approximately 60 . By definition this would be 1% higher burn than can be achieved by flying max rang cruise . For cost index higher or lower you can estimate within 1% what different from LRC would be i.e for cost index of 30 the fuel required will be 0.5% less than LRC or index 120 fuel will be 1% more than LRC fuel. Cost index value change on a given sector within day dependant on the change to the time dependant cost ( fligft time ) , overflying cost and fuel price . :ok:
25th Jul 2003, 04:58
Hi, this post is for Joe Monsoon.
I generally agree with your point of view regarding CI, but would like to Know where or how did you get the rule of thumb "60 increase/decrease in CI means a 1% increase/decrease in fuel burned" it seems to me little fuel penalty.
As far as I know overflying expenses depends on miles flown over the sector not airbone time, so CI cannot depends on it, just on DOC and fuel price.
Regards and thanks in advance.
26th Jul 2003, 10:25
ECON is for minimum cost operations
SL1 is somewhere around two-thirds of the ECON for even better fuel economy when tailwinds or time-ahead-of-schedule allows
OT1 is used for headwinds or when behind schedule
MNF and MRG values are usually 0 for min fuel or max range
Thanks for that, would you happen to have their B777-200 values?
29th Jul 2003, 14:56
A couple of years ago there was a comprehensive discussion on the FMS Bluecoat forum (with lots of driver and engineer input, including from software engineers who were involved in writing software for the boxes). The info will still be in the archive. Search for "FMS Bluecoat", and follow your nose.
1st Aug 2003, 18:29
Real long haul CI varried by dispatch from 40 to 80. On EU sectors 100.
Current job CI 60. We r doing 70% 11h FLTM+ and 30% 6h FLTM
My personal view is changing CI is the easiest way to modify the speed sched for the whole flight, as u don't need to modify Descend separately. And I believe d FMC does a better job than us - by changing CI we do not hamper it in anyway as when we use speed interv.
The Company is not too strict in enforsing CI, so I am happy to change it when I need to catch up on the sched. I use up to 200 as it still gives a good margin to unhealthy speeds. But they will soon start monitoring flights and then I will c...