I've set a cost index of 20, which I do with every flight, but the flight computer is taking me to the upper limit of the aircraft's safe speed. This has only happened after the last update. Has anyone else had this problem?

Are you using Simbrief to help calculate the cost index? Every flight is different so it will require a different cost index for each. If you’re just setting it to 20 all the time, there’s going to be discrepancies with performance because the weights and fuel will be different for each flight. If you have simbrief, I would use what they calculate for CI. 

I set cost index to 20 in simbrief.

But regardless of what is planned in simbrief, shouldn't a cost index of 99 in the FMC equal the maximum safe speed for the aircraft in flight? And a cost index of 20 in the FMC should be significantly slower than that? That's how it's always been in my simming experience (X-Plane Zibo + MSFS PMDG, until this last update).

6 minutes ago, booga said:

But regardless of what is planned in simbrief, shouldn't a cost index of 99 in the FMC equal the maximum safe speed for the aircraft in flight? And a cost index of 20 in the FMC should be significantly slower than that? That's how it's always been in my simming experience (X-Plane Zibo + MSFS PMDG, until this last update).

Yes, this is correct.  Most airlines don't adjust cost index for every flight based on specific weights etc.  If it's adjusted off of a default, it's typically because either you're already running late, or strong headwinds make a higher cost index more efficient. 

So, with a CI of 20, you really shouldn't be near the barber pole.

I used 20 tonight and was at FL300 and maybe around 0.72 on the speed.  Far enough from the barber pole.  I've never seen an issue using 20, 30 or 40, which is what I usually pick.

On 12/8/2023 at 9:05 PM, Stearmandriver said:

Yes, this is correct.  Most airlines don't adjust cost index for every flight based on specific weights etc.  If it's adjusted off of a default, it's typically because either you're already running late, or strong headwinds make a higher cost index more efficient. 

So, with a CI of 20, you really shouldn't be near the barber pole.

Just a quick question for you. I always fly current, real-world flights based off of Flightaware. They are all US domestic routes, and I populate Simbrief with the exact information that I see in FA. This is usually just the airline code, flight number, origin, destination, departure time, flight level, flight plan, and I put exactly what FA shows as  "total travel time" in Simbrief as "Scheduled Block Time".  In Simbrief, I have the default CI set up as 18 for all of the airframes.

I hit the exact departure and arrival times as the real flights almost every time and Simbrief is providing huge differences in CI for every flight. I generally see CIs in the 5 to 67 range. I always assumed that SB was calculating the CI based off of the flight time, winds, and loading of the airplane. Is that correct? I fly KBWI-KBOS quite often since it is a relatively short flight. 99% of the time, it's a SWA flight. I've seen flight times as short as 1:05 and as long as 1:30 in FA. I think I even got a CI of 80 once on that flight, which is the highest SB has ever given me.

At any rate, this implies to me that Southwest is using different CIs for different flights. I think I get the highest CIs on my morning coffee flights, which are the business commuter flights on weekdays. Is that the case, or is what I am seeing a "sim thing"?   

On 12/9/2023 at 2:50 AM, Bdub22 said:

Are you using Simbrief to help calculate the cost index? Every flight is different so it will require a different cost index for each. If you’re just setting it to 20 all the time, there’s going to be discrepancies with performance because the weights and fuel will be different for each flight. If you have simbrief, I would use what they calculate for CI. 

That's not true. The cost index does not depend on weights or fuel and certainly not on performance; it's a pure business decision if you will (trade in fuel burn for time gain and vice versa). You can fly any cost index with any kind of weight. (Of course you have to take more fuel with you with a higher cost index, because you'll burn more).

57 minutes ago, MDFlier said:

Just a quick question for you. I always fly current, real-world flights based off of Flightaware. They are all US domestic routes, and I populate Simbrief with the exact information that I see in FA. This is usually just the airline code, flight number, origin, destination, departure time, flight level, flight plan, and I put exactly what FA shows as  "total travel time" in Simbrief as "Scheduled Block Time".  In Simbrief, I have the default CI set up as 18 for all of the airframes.

I hit the exact departure and arrival times as the real flights almost every time and Simbrief is providing huge differences in CI for every flight. I generally see CIs in the 5 to 67 range. I always assumed that SB was calculating the CI based off of the flight time, winds, and loading of the airplane. Is that correct? I fly KBWI-KBOS quite often since it is a relatively short flight. 99% of the time, it's a SWA flight. I've seen flight times as short as 1:05 and as long as 1:30 in FA. I think I even got a CI of 80 once on that flight, which is the highest SB has ever given me.

At any rate, this implies to me that Southwest is using different CIs for different flights. I think I get the highest CIs on my morning coffee flights, which are the business commuter flights on weekdays. Is that the case, or is what I am seeing a "sim thing"?   

Simbrief calculates cost index by simply using the scheduled block time (as the crow flies) and the cruise speed of the aircraft model (in other words: it sets the cost index to a value that will - by calculation - make the aircraft arrive at the destination [again, only point-to-point] at the end of the scheduled block time). It does not include winds or SIDs or STARs or the loading of the airplane.
You can try it yourself: Just enter manually a scheduled block time of one additional hour plus and you'll find yourself with a cost index of 0. Viceversa if you set block time to 50%, you'll get a cost index of 99 etc.

Simbrief cost index calculation has nothing to do with how it's being used in real life, so you'd rather just enter one yourself to keep it realistic. E.g. Low-cost carriers 0-12, premium airlines 12-30 or something like that.

On 12/9/2023 at 1:51 AM, booga said:

I've set a cost index of 20, which I do with every flight, but the flight computer is taking me to the upper limit of the aircraft's safe speed. This has only happened after the last update. Has anyone else had this problem?

Probably a user error, I'm afraid. Maybe you entered 200 or you set a wrong ZFW etc.
Make a screenshot of the perf init page and the clb page, the error will most probably be right there.

Something that I noticed last night.  PMDG imports a lot of SimBrief data now, which is nice.  ZFW, Fuel, Callsign, route; It's all synced nicely.  BUT... the altitude I chose and entered into SimBrief was FL300.  I noticed after a little bit when I leveled off that the speed seemed rather fast.  I was alerted to it by the FMC telling me to reset the MCP.  I looked at the FMC and noticed the CRZ was set to FL380.  I changed the CRZ altitude in the FMC to FL300 and it slowed down considerably.  It must have been stuck in CLB mode.