My 'go to' plane is the PMDG 738, which I adore! My question is... when setting up a flightplan in Simbrief and once it is generated, it provides a CI value, which can vary depending on the airline, my question is... is it necessary to change the CI value in the setup page in the CDU (via the Menu, which, unless I'm mistaken, is set at 18 by default) in addition to inputting the Simbrief CI into the performance page? I hope I have explained this properly.

Edited December 24, 20241 yr by Rocky_53

22 minutes ago, Rocky_53 said:

which is important?

Hi, that CI 18 in the PMDG menu is just a number they chose, probably by one of the real pilots involved in testing. This CI varies wildly between the airlines; some use a fixed one across the fleet, while others use a different one for each segment. In your case, using the one provided by Simdrief for each flight will ensure you comply with fuel quantities and requirements if those estimates are accurate. So, yes, for each flight using Simbrief, use their CI. 

1 minute ago, LRBS said:

Hi, that CI 18 in the PMDG menu is just a number they chose, probably by one of the real pilots involved in testing. This CI varies wildly between the airlines; some use a fixed one across the fleet, while others use a different one for each segment. In your case, using the one provided by Simdrief for each flight will ensure you comply with fuel quantities and requirements if those estimates are accurate. So, yes, for each flight using Simbrief, use their CI. 

Many thanks, appreciated.

I load the Simbrief into the 737, and the cost index is loaded into the FMC, which is in the Simbrief Flight Plan. 

26 minutes ago, Bobsk8 said:

I load the Simbrief into the 737, and the cost index is loaded into the FMC, which is in the Simbrief Flight Plan. 

Same here.  Actually, you tell Simbrief what CI to use, then it's reflected in the flight plan (and fuel calc), then if you accept performance parameters, it's entered in the FMC (overwriting the airplane's default CI).  The CI that appears in the Simbrief flight setup page is actually the saved CI for that airframe.  Look in saved airframes / edit the one you're using / aircraft performance section.  Then look at the default cruise profile.

The CI tells the FMC how to make the cruise speed tradeoff between fast-short-time-high fuel-use and slow-long-flight-time-low-fuel-burn...based on economics..cost of an hour of flight time vs. cost of a pound of fuel.  Since this changes with the aircraft type and fuel cost (both always varying), the airlines set this for each type.  0 ==> fuel is infinitely expensive, try to burn the minimum.  500+ ==> flight time is (basically) infinitely expensive, shorten the flight time regardless of fuel burn.

BTW, CI=0 gives you max range,  CI big (like 500) gives you max cruise speed, LRC gives you 99% of the max range (a set compromise).  Or, you can just set a cruise speed, or use the RTA (required time of arrival) function, which will calculate a speed to arrive at a given waypoint at a given time.

Note that the fuel planning from Simbrief assumes you'll use the chosen CI, so if you ignore it and put your foot down, check estimated fuel at destination (PROG page) and make sure there's still enough!

If you look at page 2 of the flight plan, you'll see the effect of low and high CI on fuel burn and arrival time vs. plan.

 

1 hour ago, Bobsk8 said:

I load the Simbrief into the 737, and the cost index is loaded into the FMC, which is in the Simbrief Flight Plan. 

 

27 minutes ago, BufordTX said:

Same here.  Actually, you tell Simbrief what CI to use, then it's reflected in the flight plan (and fuel calc), then if you accept performance parameters, it's entered in the FMC (overwriting the airplane's default CI).  The CI that appears in the Simbrief flight setup page is actually the saved CI for that airframe.  Look in saved airframes / edit the one you're using / aircraft performance section.  Then look at the default cruise profile.

The CI tells the FMC how to make the cruise speed tradeoff between fast-short-time-high fuel-use and slow-long-flight-time-low-fuel-burn...based on economics..cost of an hour of flight time vs. cost of a pound of fuel.  Since this changes with the aircraft type and fuel cost (both always varying), the airlines set this for each type.  0 ==> fuel is infinitely expensive, try to burn the minimum.  500+ ==> flight time is (basically) infinitely expensive, shorten the flight time regardless of fuel burn.

BTW, CI=0 gives you max range,  CI big (like 500) gives you max cruise speed, LRC gives you 99% of the max range (a set compromise).  Or, you can just set a cruise speed, or use the RTA (required time of arrival) function, which will calculate a speed to arrive at a given waypoint at a given time.

Note that the fuel planning from Simbrief assumes you'll use the chosen CI, so if you ignore it and put your foot down, check estimated fuel at destination (PROG page) and make sure there's still enough!

If you look at page 2 of the flight plan, you'll see the effect of low and high CI on fuel burn and arrival time vs. plan.

 

Hmm, I have never found Simbrief to automatically load the CI into the FMC. I allow it to automatically generate the altitude and CI after I have inputted the pax load, then I retrieve the generated CI from the final plan and input it manually in the performance page of the CDU. Obviously finger trouble at my end!

11 minutes ago, Rocky_53 said:

 

Hmm, I have never found Simbrief to automatically load the CI into the FMC. I allow it to automatically generate the altitude and CI after I have inputted the pax load, then I retrieve the generated CI from the final plan and input it manually in the performance page of the CDU. Obviously finger trouble at my end!

I let Simbrief load everything using t he PMDG EFB, passengers, fuel, and flight plan. Just two buttons to click in the FMC. 

15 minutes ago, Bobsk8 said:

I let Simbrief load everything using t he PMDG EFB, passengers, fuel, and flight plan. Just two buttons to click in the FMC. 

Ah ha, that maybe the reason then... I don't use the EFB. It's another element that needs to be used with the mouse. I fly 99% mouse free! I was hoping that PMDG would enable some kind of function that allowed the EFB to be used on a real world tablet. I think there was talk of that at some point. That would be awesome! 

Loading simbrief on the tablet just puts the .rte file in the Flight Plans directory and the winds .wx file in the WX directory.  Packages/pmdg-aircraft-B7??/work/Flightplans and Packages/pmdg-aircraft-B7??/work/WX.

If you hit flightplan downloads after creating generating the plan and scroll down to PMDG, simbrief will download them.  Then you can select the route and download winds from the FMC.  But, of course, that involves mousing, albeit without using the tablet.

 

You can get a mouse for about$10

 

35 minutes ago, Bobsk8 said:

You can get a mouse for about$10

 

Cost index IRL is basically a number derived from operating costs/fuel costs. It varies from airline to airline the but basic concept is lower the cost index, lower cruising speed, less fuel consumption hence reduced costs but longer flight time. The opposite is true for higher cost index, faster cruising speed, more fuel burn, greater operating costs however shorter flight time. The number goes from 0 - 999. For example one of the Europe's low cost carrier uses "6" for cost index whereas other operator uses "30" on same aircraft type. 

IRL - there are few instances where crews might adjust cost index to fly faster/slower. Etc depending on situation. If they are running behind schedule then using higher cost index will result in faster speeds hence saving bit of time but at a greater operating costs (more fuel burn/engine life...etc). If there is ATC restriction of crossing a certain fix/intersection at a specified time then crews can adjust their cost index accordingly to meet that restriction. Their company's OFP (operational flight plan) will specify what result will be if using different cost index (Fuel penalty/operating costs..etc)  

In the sim however since operating costs no longer applies - you can use whatever you think is convenient for that flight. If you want quicker flight - use higher cost index or if you want to minimise fuel consumption then use lower cost index. When I am flying on 737ng in the sim, I initially use 20 for planning and initial set-up then adjust accordingly en-route. 

 

Edited December 25, 20241 yr by CAP1234

Fuel in the sim is cheap. Whack that sucker up to 500! 

https://www.flaps2approach.com/journal/2014/12/1/cost-index-ci-explained.html

You can change it during flight on performance page. 

If you have right FMC set on prog page you can change it on left cdu to see the actual effect. 

A tip I'd give if you set it way up high is to lower it way down 20 miles before your descent. This way you'll not have to worry so much about DRAG REQUIRED msgs. If you get those a lot just set CI to 1 before descent, sit back n chill to approach. 

You might want to download a copy of

https://www.togaprojects.com/_files/ugd/ed0ac6_4de9c36df622448b93db31c369d359d6.pdf

which is a database of IRL (or so say the authors) CI values for a large number of commercial carriers. These values appear to change over time depending on labor and fuel costs for the different airlines, but it gives you a sense of what actual flights might use. Note that some airlines use different CI values for specific circumstances like delayed flights.

Have fun. Best wishes to all for a most successful 2025.