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I would like to know how to calculate de best altitude at wich i

Okay. Which aircrafts, and what's the routings and your take-off weights?  :)

But if we have to get general here, most aircrafts feels comfortable at ANY weight between FL320-360 (somewhere around there) but it wont be the most optimal altitude in some cases.

Example: FL360 is a little too high for a fully loaded Boeing 767. I'm currently flying over the North Atlantic and I'm heavily loaded so the FMC has my optimal altitude at FL320. I have to fly another hour or so before I can step-climb to FL360.
Meanwhile, FL320 is too low for a light Boeing 737NG, which is likely to cruise at FL370+ if the route allows that

Also just a quick rule of thumb.  Don't know if this is correct globally, but it certainly states so in the KLM pilot's manuals:

For IFR flights:
Even flight levels when flying headings between 180 and 360 degrees, e.g FL300, FL320, FL340.
Odd flight levels when flying headings between 001 and 179 degrees, e.g FL310, FL330, FL350.

The initial top cruise altitude will be set based on the heading sector for the majority of the flight, although it is subject to alteration by regional ATC.

Hope that helps.

Hussein.

Hussein, those levels are RVSM (FL290-FL410), and not all parts of the world have that implemented yet, although Eurocontrol has been doing it since 2002, hence your KLM manuals states those flight levels

Hello.  Thanks for clearing that up Nexus.  As youmay have guessed, I am not a real-world pilot, but was fortunate to have a pretty damn good flying experience complete with trimmings on a trcent trip to Amsterdam, hence my access to the flight manuals, etc.

I fly the 737 from MHTG to KMIA
the flight planner programs an altitude of 9000ft!!!

ofcourse this is too low!  i guess 32000 to 39000ft would be the correct altitude.

but thats only my guess cause I want to know how to calculate the right altitude.

and why does the flight planner give me so low altitudes and how can i avoid this cause I dont know you guys this is a little annoying....

[quote]I fly the 737 from MHTG to KMIA
the flight planner programs an altitude of 9000ft!!!

ofcourse this is too low!

But that's so dumb...I thought "high altitude airways" meant +18000ft?

If you find the real performance values for your aircraft, they may not help you because the FS model may not be accurate enough.

I prefer to do a flight test of the FS model to see how it actually performs in the simulator. Here's how I determine the maximum cruise altitude of any FS jet aircraft:

- First, be sure the aircraft is full of fuel at max takeoff gross weight.

- Takeoff and climb to the highest possible altitude, using the autothrottle or max climb power.

- Reduce the climb rate (VSI) as required to maintain the correct indicated airspeed (or Mach number).

- I measure ceiling altitude as the point where the climb rate is 1000 fpm and airspeed (or Mach) can no longer be maintained.

This is just the way I do it. The climb rate at ceiling altitude is somewhat arbitrary. Someone else may use a more precise definition for minimum climb rate, but since the FS model isn't perfect, the climb rate definition doesn't have to be perfect.

If your flight is short and the fuel load is reduced, then the ceiling altitude will obviously be higher. To know for sure, rerun the flight test at a lower fuel weight.

Give it a try and see how close you get to the published performance of your B737.

Regards,
JerryH