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View Full Version : 787 Cost Index


Cgarcia0458
06-12-2018, 06:21 AM
Hey guys, sorry if this is off topic, but Iím a PPL working on my IFR and I dabble in the simulators now and then. Quick question, what cost index does AA use on the 787-8 and -9? Is it standard or does it vary with the route. Thanks so much!


Twin Wasp
06-12-2018, 07:51 AM
Not AA but I'm going to say it will vary. Even the same route on different days. Say you have a flight during the winter into the jet stream. A higher CI will help keep you on schedule. The return leg could have a lower CI to take advantage of the tailwind. Different season with less winds the CI might be the same both ways.

Sliceback
06-12-2018, 09:17 AM
If you're on time, or early, it looks like it's 18 or 19. Gives you an .84 cruise.

Late? Much higher. CI-300 gives you a .86 cruise.

Most of the flying is done at the slower, lower cost index, cruise speeds.

You might see minor adjustments but the on time Cost Indexes don't change much. But the FMC uses the tail wind or head wind and adjusts the cruise speed but even then it tends to be minor changes. A low cost index (CI range 30-39) might have a cruise speed on the 777 of .829. Tailwind might drop it to .828 if at all while a significant headwind might increase it to .836.

And all speeds adjust via the CI if you're at your optimum altitude. If you're at optimum altitude a standard CI of 30-39 gives you .83 (+/- for headwinds). If you're 4000' below OPT ALT your ECON cruise mach will lower, perhaps .815 (+/-) and decreasing to .77 at the end of a 10 hr flight.

So CI is fairly constant if you're flying at OPT ALT. It makes some adjustments for headwinds and a smaller adjustment for tailwinds. If you're at a low CI reductions for tailwinds don't occur since you're already at LRC (long range cruise).

Flying 4000' below OPT ALT using the planned cruise mach had an over burn of 5,000 lbs. Using ECON CRZ (adjusted by CI and off altitude cruise) reduced the projected over burn by 50%.


Overwater/non radar we typically fly an assigned mach number. When that happens the CI, and headwind/tailwind adjustment from the FMC, is meaningless.


Varks
06-13-2018, 04:56 AM
Cost index has nothing to do with being on time. It is about fuel burn. Strong headwind high cost index. Tailwind low cost index. Plane does not know on time. Plane knows efficiency. Example. If you are late and have a tailwind you will still see a low cost index. It is up to pilots/dispatchers to increase this to get back on time. Increased fuel burn. Manual says stick to the planned as much as practical. If I am early I play with the number/altitude to see if fuel burn goes down. If I am trying to make a commute it goes 99. Just kidding of course. Some pilots insist company monitors what you put in and will get in trouble.

I always try to save fuel. Not so much for company but for my own personal fun. Same as when I drive my cars. I kick my wifeís ass in efficient driving. She is a much better driver than I am but less efficient. I have been a hyper-miler since I started driving.

Sliceback
06-13-2018, 08:36 AM
The company's dispatch system operates with on time as the #1 factor. It attempts to meet on time performance by increasing cruise speed. At the airplane that is achieved by the flight plan having a higher CI which gives a higher cruise speed.

After on time is met the next factor it attempts to achieve is the lowest cost which is closely related to the lowest fuel burn.