How to select a "good" cruise altitude?

[MasterTRL]

Hi Guys,

i´m trying to figure out how i should proceed to select a good cruise altitude. I read some things about planes having a designated max alt for a specific weight, say FL250 is max alt with 30000lbs (i made these values up!).

Is there some kind of chart or table where i can check how hi i can fly? Or a formula to calculate?

How do YOU decide about the altitude?

Cheers

Chris

[Japo32]

Well.. not beeing a good pilot.. and still learning.. what I usually do is take experience from the plane. Make my numbers and try to have a "formula" Not always you burn the same ammount of fuel. Depends in temperature, winds, weight.. etc.

But I choose the altitude normally by the winds in altitude. Maybe it takes more fuel to reach "that" altitude but if the wings are more tail winds strongs than other lower.. then I preffer to waste that extra fuel to preserve over the trip.. if the trip is long enough of course.

[MasterTRL]

Hi J,

thanks for your opinion. Actually i thought that including the wind into the calculation would be my next step after i have figured out how high to fly with a certain weight.

However i found out so far that there should exist a "performance manual" for every(?) plane which has the information about altitude in relation to weight. I was wondering if you would posess such a manual since i did not find it online, at least not for free.

Also i have noticed that the FMC gave me advice for the altitude in the legs list. Is this a calculation or are these just standard values? For example on my todays flight from EDDM to LGKR, about 600nm, it said i should ascend to 250 for cruise. This sounds realistic to me but i can not judge if it is really the right altitude for my weight of 48000 at this moment.

Cheers

Chris

[guym-p]

However i found out so far that there should exist a "performance manual" for every(?) plane which has the information about altitude in relation to weight. I was wondering if you would posess such a manual since i did not find it online, at least not for free.

Yes: search for "Performance Data" or "Flight Planning Data". For small aircraft, they tend to be a section in the Flight Manual, but for airliners they are usually a separate book. The good news is that a lot of people don't realise what they are. Flight manuals tend to fetch high prices on eBay because they are so obviously interesting or valuable. Planning data tends to be pages and pages of tabulated data that look dull unless you know what they are. I have bought several original copies on eBay for next to nothing.

The basic assumption for a jet aircraft is to fly as high as possible, but weight, duration, weather, and traffic might force the pilot to choose a lower altitude. Even if you can not find planning data for the aircraft you are interested in, most flight manuals have charts showing maximum altitude against weight, or maximum Mach against weight and altitude. Having established the boundaries, you could then carry out test flights to see how much fuel is burned during a climb with different starting weights, also during cruise, and then decent. Armed with those and a spreadsheet, you should be able to create your own planning data, and work out the most economical altitude to climb to for a specific route.

"Cruise climb" was popular with early jet airliners: the idea that it is economical to climb to FL320 (for example) and then to let the aircraft rise to FL350 or higher as fuel is burned off and it becomes lighter.