737-800 Q&A

[BrianW 124]

Not sure how you’re coming up with 5-10 minutes. The TAS difference at cruise altitude between .77 and .78 is only about 6 knots. When cruising at more than 7 miles a minute that’s under 2 minutes for a 2 hour flight.

 

Keep in mind the other side of the CI ratio is fuel. If the CI of 10 used less fuel than a straight .78 cruise at a cost of only 2 minutes the airline bean counters might consider it a win. On the other hand if your aircraft is wet leased those 2 minutes might mean more since someone else is paying the fuel bill. In reality neither the time or fuel values change too much on a per flight basis, but when you scale it to an entire fleet it can make a huge difference.

[Pe11e 812]

Thanks for your clarification, it's now much more logical to me, and on top of all I can rely on PFPX again.
I'm not sure neither how I managed to come up with 5-10 minutes. 

 

That is exactly the reason I want to use CI, to save the money using FsPassengers. I guess I can stick with CI 20, which is low cost. Who uses CI 10 or 5? I heard that Ryanair uses CI 5?

[JWNoctis 4]

Optimum CI is a function of fuel cost, time cost and fixed cost - If fuel cost is high and time cost is low as is the case with most LCC, then CI would be low. Supposedly real-world airlines had tools to calculate them, but I'm just parroting what I heard.

 

EDIT: Too low a CI would result in a considerably slower cruise speed closer to those of Classics', and probably annoy enroute ATCO's in busy sectors as they try to fit an aircraft cruising at .75 into a stream of other narrowbodies cruising at .78-.79. Way much better than VLJ's cruising at .55 up to FL410, but still...I think I once read something about that.

[ExNusquam 11]

 

 

Way much better than VLJ's cruising at .55 up to FL410, but still...I think I once read something about that.

 

Believe it. This picture was taken at FL390 on a good day. 

[JWNoctis 4]

That's a good tailwind, at least...Still somewhat faster and much higher than most turboprops. Guess that's how most of them sold.