http://www.airlinepilotforums.com/te...tml#post844479
From Boeing:
A recent evaluation at an airline yielded some very interesting results, some of which are summarized in Figure 4 (see previous page). A rigorous study was made of the optimal CI for the 737 and MD-80 fleets for this particular operator. The optimal CI was determined to be 12 for all 737 models, and 22 for the MD-80.
The table (see fig. 4, on previous page) shows the impact on trip time and potential savings over the course of a year of changing the CI for a typical 1,000-mile trip. The potential annual savings to the airline of changing the CI is between US$4 million and $5 million a year with a negligible effect on schedule.
SUMMARY
CI can be an extremely useful way to manage operating costs. Because CI is a function of both fuel and nonfuel costs, it is important to use it appropriately to gain the greatest benefit. Appropriate use varies with each airline, and perhaps for each flight.
Seems as if Boeing can't make up their mind. Some random airline operating MD-80's and 737's (Delta, American . . . any obvious international carrier I'm missing here?) paid Boeing lots of $ to do a study of the best use of CI, and Boeing seems to recommend a constant CI for each fleet, but reminds us that varying the CI
may be the best of all. Why would it not, if you had the ability to do so (some fancy computer cost algorithm to model the best CI, which you'd surely have after paying Boeing to do a study of CI)?
See the complete Boeing article
here, including the graphs I don't know how to post.