Altitude Hold (747-400)

[NSEU]

Gentlefolks...

The manuals say that if Altitude Hold is selected in climb or descent that the aircraft will overshoot, but will return to the altitude at the time at which the button was pressed.

I've been told that the 767 doesn't always (completely) return to this altitude. Is this the same for a 747-400. If so, would anyone have any typical error values? Do higher V/S's result in the greatest errors... or might there be other factors involved?

I would ask our own pilots, but the only chance I get to see them is during preflight checks (not an ideal time).

Thanks!
Rgds
NSEU

[Intruder]

On the 744 it returns to the altitude, and I find is does so very accurately. However, if the vertical speed is high when you push it, you may not know EXACTLY what the altitude was when switch contact is made.

[FlightPathOBN]

NSEU,
Intruder is correct, it will return to alt...but its a function of when depressed. If you are in level flight, it stays, but in climb or descent, it must recover from such and maintain, and depending on your FMS manufacturer, the +/- value can make a difference.
I have worked with some that have a different accuracy on climb vs descent, and said accuracy can be 10's or 100's in the rounding factor.

Perhaps your application can help in the response.

Cheers!

[NSEU]

Thanks, guys.

but in climb or descent, it must recover from such and maintain, and depending on your FMS manufacturer, the +/- value can make a difference.

FMS or FCC? ALT HOLD on the 744 should be an autopilot function (purely).

I have worked with some that have a different accuracy on climb vs descent, and said accuracy can be 10's or 100's in the rounding factor.

But if rounding applies, then there is a possibility that aircraft won't return to the exact altitude at which the button was pushed(?).

Unfortunately, this is a general interest item and trivial compared to AOG/operational stuff, and we don't really have channels of inquiry for this kind of thing.

Cheers
NSEU

[Intruder]

Once again, HOW can rounding be an operational factor when you can't determine EXACTLY when the switch contact is made when you press the button? If the altitude is stable, any rounding will already have been applied, and the altitude will remain whatever it is at the time you push the button. If NOT stable, it will stabilize at an altitude somewhere between the altitude at the beginning of the switch press and the end of the push stroke. I can't see how you can get more "exact" than that, due to simple mechanical and human reaction limitations.