What's your cost index?

[radarlove]

I've never seen very much information on how cost indexes are derived. I know that it's cost of fuel/cost of airplane per hour, but that doesn't explain the actual number that folks put into an electric jet.

What do you guys use for different models of Boeings? Airbuses? Jungle Jets?

Are the numbers roughly equivant between models or manufacturers? Or are they unique to each type?

 

[180ToTheMarker]

For the 717 its 25.

 

[atldc9]

We have historically used 30 as a default setting on the 717 at AirTran. Lately though, the company switched to 25 to more closely align with long range cruise. We also have a program to use 99 on selected flight to try to mitigate the impact of unusually large headwinds on hub performance.

The 717 will take anything from 0 to 999 for a cost index.

 

[fxbat]

4 the 737-8
We use 36. It’s a touch above long range cruse.

 

[Saabslime]

Standard on the airbus is 30. On some flights coming back from the east coast or if we need to make up some time I've seen 50 or 70 used.

 

[sf340flyer]

At AS we use 15 for the NGs and 25 for the -400. I have flown EMB 135/140/145 and the ERJ 170, and they don't use cost index.

 

[DTW320]

Standard on the airbus is 30. On some flights coming back from the east coast or if we need to make up some time I've seen 50 or 70 used.

Standard on the 320/319 at NWA is 60.

Or 600 if it is the last leg and you have a tight commute......"What?, Mr. CP, you say I had 600 in the CI on that leg? I must have accidentally hit an extra zero.....won't happen again...."

 

[typhoonpilot]

We're somewhere between 60 and 80 of late on the 777. It used to almost always be over 100, but with fuel price increaes it has come down significantly. The net effect is slight reduction in cruise speed from .84 to .83 plus very slow descent speeds. My company computes the cost index for each different leg based on current fuel costs at that station.

Typhoonpilot

 

[scarface]

On the 767 at ABX we use 80.

 

[RideandDrive]

80 on the 747-400 at Polar

 

[CCDiscoB]

Md-11 200 =.83

 

[mnboyev]

Top Secret.. LCC Confidential to ensure 'edge' over legacies... All in fun....

I like using the RTA Function to keep block times equal to schedule. Works good.. keeps ya from waiting for a gate in MDW..

 

[radarlove]

Well, I guess I asked the wrong question. What does it all mean? What is the difference between a 60 and a 25?

 

[AAflyer]

Well, I guess I asked the wrong question. What does it all mean? What is the difference between a 60 and a 25?

Cost Index and how we use it.


With the advent of FMS/PMS, operators gained the ability to make an economic decision regarding speed based on other costs, but including fuel. This was done with the development of a formula called Cost Index. The formula seems simple enough. It is the sum of the Variable Crew Costs (cockpit and cabin) and the Variable Maintenance Costs divided by the fuel costs in cents per pound. Fuel costs seem easy enough to calculate although it can get a little complicated when tankering effects and hook-up fees are considered. Variable crew costs get very complicated when one considers the wide range of pay on any given flight. (Seniority, gaurantees, volunteer flying, trip credit, actual or schedule, minimum daily, reserve status,etc. That is just for the cockpit, the cabin having their own variables.) Variable Maintenance Costs are even more difficult to calculate as some airplanes are under warranty or parts of them are under warranty and many components are on a cycle basis for change or repair rather than hourly.

In consideration of this complexity, it still has been possible to assemble the data that at least captures the spirit of the formula. Our Phoenix Flight Planning program can do this. The computer can generate a Cost Index and when entered into the PMS/FMS will allow a flight to be flown at its most ECONomical speed. (Perf on PMS MD-80s.) The computer will adjust speed in climb, cruise, and descent and should yield a minimum total cost for the flight. If fuel is comparatively cheap, it will fly fast ( have a high CI.) If fuel is expensive, it will fly slow (a CI more toward zero.) The range of speed from fast to slow is from just below MMo to MRC. It normally flies between MRC and LRC. In other words, it tries to capture as much of that 1% of the burn that we talked about earlier.( That 1% being the fuel used between MRC and LRC.)

The following discussion may add a little cloudiness to the subject. Let's examine a flight. STL-LAX. As soon as the flight departs STL and climbs at 320 knots, the CI calculation is invalidated.( The flight is still operating with an economic consideration in mind but the consideration is to help increase the volume of the STL airport and not to minimize the total cost of the flight). As you can see, all flights operating into and out of STL cannot have a correct CI calculated for it because of this speed intervention. The same is true of flights on oceanic where a portion is flown at constant mach.
We do believe with some massaging of the formula that we can get fairly accurate CIs on these flights. Testing is continuing and we hope to have something in the works later in the spring. We do have some flights where CI calculations are correct and we can expect to see that concept implemented before too long.

The way we have been operating is that we have CIs that emulate LRC as closely as possible. That is why you have been seeing a CI of 30 on the MD-80s for example. It is fair to say that with fuel costs rising, the airline should be operating at a slightly lower speed. This decision has to be made very carefully however, as on time performance could be impacted by that decision.

We will be using a concept based on a Boeing recomendation called "Generalized Cost Function". This GFC takes the Cost Index formula and incorporates a consideration for on time arrival. Thus it takes into account all the costs mentioned above plus a cost associated with on time arrival excursions. The number you see will still be expressed as Cost Index and GFC will not be displayed anywhere.

AAflyer

From our operations department explaining CI.

 

[FoxHunter]

Md-11 200 =.83

Close, but not exact. You will see most guys flying at CI 200 but in most cases that will not agree with your FP/R. The flight plans are almost always at M.83, not ECON. On the rare occasion I have seen a real ECON flight plan it was within Europe. On the heading line where it normally says CRZ M83 you will see CRZ 200. I've never seen an ECON flight plan on any of the longer legs. The problem with flying CI 200 is that as a head wind increases the speed may increase to as high as M.85 with the corresponding increase in the fuel burn. You will also find that the FMS will want to climb to the next altitude 45 to 60 minutes later than using an Edit M.83.

 

[FoxHunter]

We're somewhere between 60 and 80 of late on the 777. It used to almost always be over 100, but with fuel price increaes it has come down significantly. The net effect is slight reduction in cruise speed from .84 to .83 plus very slow descent speeds. My company computes the cost index for each different leg based on current fuel costs at that station.

Typhoonpilot

My company computed it to be 200 for the MD11 in 1991 because it was close to M.83.

 

[Alcatraz]

FoxHunter just hinted at this, but nobody else seemed to mention it: cruise speed (and I believe climb speed) is dependant not only on weight and cost index but headwind component when using ECON.

You may notice this in the sim during a LOFT scenario when the instructor adds a 250 knot tailwind... the airplane will slow way down, and T/D moves back and really screws you up when the winds are removed just prior to T/D. You'll also notice speeds that are faster going westbound (with a headwind) than going eastbound (with a tailwind).

radarlove: To answer your question simply, with all other factors being equal, a LOWER cost index results in LOWER SPEEDS, usually due to HIGHER fuel costs when compared to hourly costs.

 

[FL420]

Airbus published an outstanding article in their FAST magazine that has the information you seek. It is a 108 page .pdf file found at:

http://www.airbus.com/store/mm_repository/pdf/att00006418/media_object_file_FAST37_full.pdf

It covers the Honeywell FMS's found in most of the Airbus models as well as in many Boeings.

 

[SkiFishFly]

My personal cost index is way up there...

Unfortunately it is still cheaper to keep her. She is walking a fine line these days though.

 

[TWA Dude]

One more detail: many airlines have us cruise with a CI but climb and descend at a specific airspeed, ie, 300KIAS below Mach transition.