How does PFPX determine cruise altitude ?

[Herbert30 2]

I only have PFPX since a few days and so far I made a few flight plans.What I miss is the cruise altitude - the one I have to enter into the CDU - and where can I find it.

The OFP indicates a initial altitude ( what ever is meant by this expression ).

The way I understand the cruise altitude starts at the T/C and finishes at the T/D.

Can anybody explain.

Herbert30

[Mad Dog 5]

Hi

Initial Altitude is your first altitude to climb to (before possible changes due to airway restrictions or performance). This is what you enter into your FMC at the gate.

[Pierre95 14]

Hi,

As said Mad Dog, initial altitude is the first optimum FL.

Then,as aircraft weight decreases, it is increasing (Step climb).

You have to enter initial FL in FMC before takeoff then during the flight you can modify it in the respect of RVSM if needed.

Hope this help

Pierre

[Herbert30 2]

Hi,

As said Mad Dog, initial altitude is the first optimum FL.

Then,as aircraft weight decreases, it is increasing (Step climb).

You have to enter initial FL in FMC before takeoff then during the flight you can modify it in the respect of RVSM if needed.

Hope this help

Pierre

Hi,

Tanks for the info.I have a follow up question.How then is the max crz altitude determined ?

Herbert

[Emi 5161]

Hello Herbert,

There are several ways to determine this altitude.

In the Boeing 777 FCTM it says that the maximum cruise altitude is the maximum altitude at which the aircraft can climb while maintaining a manouver margin of 25° bank +15° reserve.

Or in other words: If you're climing the airdensity and therefore your lift decreases. If you're banking your lift will decrease further.

You always need to be able to do 25° banks. As some human error or some other reasons might cause a stronger bank angle Boeing descided to include a 15° margin until the aircraft will stall.

Therefore they said that the maximum altitude the is the altitude at which you can bank 25°+15° margin without stalling the aircraft.

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On the other side in the theoretic lessons for my PPL I learned that the maximum altitude is the altitude at which the aircraft can only climb with a climb rate of 200fpm.

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As you can see there are several different ways of determining a maximum altitude. Now we have to wait and see what the PFPX developer says which way PFPX uses.

[FlightSimSoft.com 283]

The maximum altitude is defined in the aircraft performance file.

For those generated by us, this altitude is the maximum altitude given by the performance output of the given aircraft type.