Boeing VNAV

[JAMES WEBSTER]

Hi guys,

I have noticed that the Aircraft can some times fly through the VNAV limit of
250Kts below FL100 in the climb. Sometimes to 270Kts. Flaps retracted on
schedule etc. Is this an issue in the aircraft.txt in the CDU?

James

[Enrico Schiratti]

> I have noticed that the Aircraft can some times fly
> through the VNAV limit of
> 250Kts below FL100 in the climb. Sometimes to 270Kts.
> Flaps retracted on
> schedule etc. Is this an issue in the aircraft.txt in the
> CDU?

If it is doing 6000 ft/minute in climb and it is doing more
than 250 knots, then you might consider reducing the climb
thrust a bit... i.e. use CLB-2 or derate it. Some
flightmodels are overpowered.

Ciao

Enrico

[Michel Vandaele]

Hi Enrico,

Additional with my émails concerning the vnav thing, I receive the info from

the real life, that VNAV is maintaining the set mcp speed (V2+10 or 20) till

the flap retraction altitude.
When reaching that altitude the speed bug is always set to VREF+100.
In the case of the B744 (from 270.000kg T/O weight on, that's higher than
250 knts with a clean aircraft).
Therefore crew has to ask permission for height speed to the ATC.

As you know, actually you set the speed directly to 250 kts in PM, once A/P

is activated.

Hope this helps a little to understand the complex working of VNAV in B744


Ciao

Michel

"Enrico Schiratti" wrote in message
news:384363.77131@wb.onvix.com...
>> I have noticed that the Aircraft can some times fly
>> through the VNAV limit of
>> 250Kts below FL100 in the climb. Sometimes to 270Kts.
>> Flaps retracted on
>> schedule etc. Is this an issue in the aircraft.txt in the
>> CDU?
>
> If it is doing 6000 ft/minute in climb and it is doing more
> than 250 knots, then you might consider reducing the climb
> thrust a bit... i.e. use CLB-2 or derate it. Some
> flightmodels are overpowered.
>
> Ciao
>
> Enrico
>