Cost Index - Trip ?

[Jambock 0]

Hello, I have a doubt with the COST INDEX B737NGX, that I can not solve.

The Cost Index is 20-25 standard for B737, but when I set up the aircraft with a weight (about 125.000Lb Gw) and put the Cost Index of 25, the field TRIP gets a very low altitude.

I believe this is not normal. Something is wrong, but I do not know what it is.

 

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I appreciate the help.

[wisefox7524 9]

How long is the trip? If it's not very long, you're not going to have a very high cruising altitude.

[rsvit 16]

FMC takes into consideration lots of things to calculate trip altitude. Not only weight and CI.

25 is normal figure for cost index. You can enter random CRZ ALT and set T/C ISA DEV or temperature for more accurate calculations and reset new cruise altitude.

 

On short flights distance, airports elevations and wind would influence trip altitude (usually for trips shorter than 300-350nm).

[Sekstifire 10]

...

The Cost Index is 20-25 standard for B737,...

Its actually a bit higher than most companies use these days, but it is of course well within the normal range so to say. Generally speaking, a lower cost index will take you quicker to your cruise altitude, which *might* give you a bit higher TRIP

[scandinavian13 5,192]

I believe this is not normal. Something is wrong, but I do not know what it is.

 

Why do you believe this is not normal?

What was the route pair, or what was the distance?

 

If you don't think something is normal, please give some type of explanation as to why not. It helps us help to solve the issue.

 

 

That aside, if you have a higher weight, a shorter route, and a lower CI, you're going to be lower. FL240 isn't incredibly low. From DCA-LGA (211nm), the max alt (ATC imposed) is FL210. Similarly, the flight from BWI-ORF (145nm) is routinely flown at around 14000'.

[pcubine 143]

Jambock

 

I have flown the PMDG 738 many times between KMIA and KTPA a distance of about 200 miles. Payload 31000 lbs, fuel 12000-13000 lbs, cost index 20. FMC comes up with a altitude of FL240 northbound and FL250 southbound. Same as American Airlines which has 5-6 flights in each direction daily using the 738. I think the real world verifies the PMDG NGX.

 

Michael Cubine

[Dominicoben 0]

Give us all the other factors". As said, some flights are as low as 14,000f