Cost Index....?

[Guest]

It seems the manuals for PIC don't really go into what the cost index is. Two questions:1) What is cost index in real life?2) Does this parameter effect anything in FS and/or PIC?Thanks

[Guest Muppet22]

HiCost index is company specific and maybe sometimes even route specific within the company. BA generally use a CI of 40.The CI is basically a figure to illustrate the balance used between speed and fuel burn/economy/efficiency.The lower the CI the lower the cruise mach #, hence lower fuel burn. 40 seems to be the best balance.

[Guest jase439]

I think Eric said AA typically uses a CI of 80.

[DShutt]

Rob Hall ACA856 uses a cost index of 800. LOLOkay, okay... kidding. I WAS USING 800.But Rob? Will you please do the honour of blessing us with your dramatic reading of the TRUE meaning of CI....DSaka LDCVA3339

[Guest hvanleusen]

Hi,This could be interesting too:http://www.avsim.com/dcforum/DCForumID43/4103.html :-)Long time ago!Hope it helps!Hans van Leusen

[Guest Iz]

CI = Time cost / Fuel costIf you have a flight where time is more important than the fuel costs, you fly a high cost index. (Max = 999)If you have a flight where time is not that important but the fuel costs are, you fly a low cost index. (Min = 0)That's all there is to it.Our company uses 70.Iz

[Guest]

I am not sure if it is correct or not in real world, but the PIC767 FMC will allow Cost Indexes much higher than 999. I have used CI 1500 at times which gives a climb speed of about 325kts to Mach .819 CLB/CRZ. Descent speeds were about the same.If I want a higher CRZ speed, I usually just ammend the VNAV-CRZ page to Mach .8xx up the the max around .84.From what I understand, the PIC FMC Cost Index calculation is not as complex as the real thing...CRZ speeds do not change in accordance with weight reduction in flight, etc.Rob.

[Guest Iz]

Hmm, could be FMC system related. Ours only goes to 999. I'm not sure if the figures at higher CI's correspond though.For example, our normal CI is 70 on the 757 which gives a no wind speed of about 312 kts / .798M.On some flights, we fly a CI of 300 and the speeds go up to around 343 kts / .818M.At CI 100, IAS during climb and descent will go up to 330. So the machine calculates that flying high IAS during climb and descent will benefit you greatly. So if it's already at 330 @ CI 100, I don't know why 767PIC sets 325 @ CI two zillion. Maybe Eric just never flew at higher CI's? We can only guess.For obvious reasons, the IAS figures that CI 200+ gives are undesirable, since they hug the barberpole. In turbulence, you're way above turbulent air penetration speed and you can easily get an overspeed. In the descent, you don't have much room for error if you're high off path (speedbrakes the only option).But anyway, that's what it comes down to. The 757 and 767 are both conventional planes with the same aerodynamic principles so I don't see why the resulting speeds should be so different, maybe some 767 drivers know the answer. Machnumber at CI 999 is probably around .83 (since anything above that, you're burning fuel like a madman due to the rapidly rising mach drag).Iz

[Guest]

I would suggest for the 'layman' use of the CI in the PIC FMC, that the original suggestion of CI 80-90 should suit 99% of your flights. This will give you a nice blend of economy and performance and seems to be the best of both worlds as posted by the designer. Only the long hauls I would suggest using CI 20-50 as I have seen the Aussies, et al, do on occasion to stretch out that Long Range Cruise (LRC calcs not being modelled in the PIC FMC).If a PIC pilot wants to put the pedal to the metal, leave the CI alone and simply change the VNAV-CRZ page to the desired SPD...or use SPD intervention on the MCP I suppose...I tend to use the FMC to control SPD when in VNAV, not to meddle with the MCP in regards to speed...preference...beautiful thing with Boeing is there is three correct ways to do the same thing and they generally all work great in any situation...unlike the French auto-pilots (name witheld to protect the guilty).God, do I babble, eh.Later.Rob.

[Guest Martin]

>Hmm, could be FMC system related. Ours only goes to 999.It is. Some go to 999 and some go to 9999 ("PIP and Pegasus FMC" it says in the manual).Martin767 fetishistIt's a lot like life and that's what's appealing

[Guest Iz]

So theoretically, the ones with CI max 9999 go ten times as fast as the ones with 999 max?? :) Naah..Seriously though, there's no noticable difference between CI 100 and 101, who thought up "Hey, let's give them even more accurate control over the CI". I imagine the difference between CI 1000 and 1001 is ten times less noticable.. Oh well....

[Guest Martin]

So many choices these days! ;-)Martin767 fetishistIt's a lot like life and that's what's appealing

[Guest anthonyj]

According to my notes taken during training on the basic FMC (Boeing software) CI 0 is the equivalent of maximum range cruise, CI 999 is the equivalent of MMO. It described Cost Index as time (operating costs) over fuel costs (t/fc).

[Guest HPSOV]

Most of what has been said is right.Important to remember that the relative cost of fuel/time will vary from airline to airline. I am not sure if different airlines program their FMC's to allow for this, or if the speeds generated by a given cost index are set by boeing.In my airline we use cost index 40 for all international ops, unless this will result in the flight being late, then the cost index will be increased as reaquired to maintain schedule (up to a max of 250). For domestic ops a cost index of 125 is used, regardless of flight time.In real aircraft the speed generated by a given cost index will vary with changes in weight, temperature and wind velocity (the speed may vary as much as 0.02 based on wind speed alone).A cost of index of 40 usually results in a speed of .78-.79. 125 will give you around .81, and 250 about .82-.83. Anything above 250 usually gives a speed above 0.83, which is too uncomfortable for the 767's autothrottle. On a recent flight the speed got to 0.851 in light chop with the FMC commanding 0.816, you have to be very careful!Our climb speeds will always be too high at cost indicies above 100. A cost index of 150 will give a climb speed of around 345/.83. This is always reduced to 320/.82 at the most, less if you're climbing into a jet-stream.At the end of the day cost index is great, but schedule is more important, especially with many of our passengers connecting with other flights. By the same token it costs a lot to go faster, it must all be part of your management of the operation, and pre-flight fuel ordering.