cruise altitude

[ex902]

hi everybody;
this is my first message to this forum...it looks like a wide range participated forum that I felt myself in a heaven :) so first of all best wishes for everyone...

my question;

I am speaking for airliners;

I need to know that is there a rule of thumb about to select the best cruise altitude due to the range...
For ex., for normal condition (all factors are average; weight, weather, time, etc); we have a range about 1000 km, do we need to climb to 37000 ft (or lets say around 33000 ft)...or what would your answer for 500 km. is there a min range to think to climb to 33000 ft?

I have limited data, associated with a B757, and according to that data, the airliner needs to fly 125 nm (231 km) to reach the 37000 ft and another 130 nm (240 km) to descent from that altitude; so the sum is about 470 km. I will base my research on this data and I try to figure out how many additional range would make the flilght economic for flying at this altitude...

other words; can we speak about a start point of range to be able to use the high cruise altitude ?

sorry about the long message but I hope it is sufficiently understandable

Enis

[BelArgUSA]

Hola Enis -
xxx
Many factors to consider as to FL level selection. All planes different.
And for same airplane types, how heavy are they...?
Climb/distance to TOC cruise FL depends mostly on their weight/payload.
xxx
With a heavy 747, the best I could hope was some FL280 initially.
And might take some 150 NM to get there.
With the 727 - medium payload, short distance, 120 NM might be ok.
And FL 310/330 was fine.
xxx
The only "somewhat" general rule is point of descent.
With all types of jet airliners I flew... 3 times the FL for distance to start descent.
As example - FL 350 = 105 NM for descent. Correct some for winds aloft.
Using the above data, you could derive an approximate FL selection.
xxx
:8
Happy contrails

[Old Smokey]

ex902,

Welcome to PPRuNe!

Your Flight Planning data should provide you with the information that you need, but a "quick and dirty" cruise level is approximately 1000 feet for each 10 miles of distance, up to the optimum level.

For Example, if you are planning a 310 nm flight, 31000 feet would be a good "rough" level to begin examining wind gradient etc. to refine it further.

That works pretty well in ISA+15 environments for aircraft in the B757 league, but beware, all aircraft are different!!!!!

Regards and Welcome,

Old Smokey

[barit1]

A short-range operator in the Far East once ran some sums from the performance book - and quickly concluded that least fuel burn resulted by climbing until they intersected the descent profile.

I managed to convince them this was not a good idea - mostly because of shock cooling, dropping from MCL (high EGT) down to idle midway on every flight. They relented and included a short 5 or 10 min. cruise segment.