View Full Version : Airbus FBW family - flight plan predictions

10th Jul 2004, 08:16
Please would anyone advise:

When a flight plan is first loaded and altitude constraints are shown the intervening waypoints altutdes are then predicted.

In the climb phase will a predicted altitude ever be higher than a subsequent constraint?

Similarly on descent will a predicted waypoint ever be lower than a subsequent constraint.

The answer would seem obvious (that a smooth path is always predicted) but I have been advised that this is not always the case.

Many thanks

11th Jul 2004, 21:15
It all depends on what the entered constraint requires.

If, during the climb for eg, the constraint is a minimum altitude by point x, but the aircraft can achieve higher, then the prediction will be higher than the constraint. Similar, but in reverse of course, for the descent.

If the constraint requires 'AT' a particular height (and it's achievable!) then prediction will be exactly that.

Hope this helps.

Port Strobe
12th Jul 2004, 16:18
AirbusFan, out of curiosity could you please elaborate on the instances you've been told of where the system logic doesn't behave as expected? Is it a pilot/engineer that told you of these accounts? I'm just interested to hear how such an inherently simple piece of system logic can go wrong, it seems strange.

Thanks in advance

12th Jul 2004, 21:58
Thanks for your help and interest.

I think it may be more a case of third hand mis-communication.
FlapsOne has confirmed my understanding.

Is the logic really that simple?