Claybird.
We are in different universes, perhaps I was not clear in my request.
We are on descent. LNAV VNAV path, on profile. ATC give us a vector and off we go away from the magenta line.
Leave the LEGS page until we have something to aim at.
In the meantime the auto pilot/FMC is following some data for descent. The derivation of that descent profile cannot be accurate as neither we, nor the FMC knows what is next to happen.
How far from the magenta line can we go before that data is invalid. At this stage we still have a vertical deviation indication and the autopilot has kept that zeroed.
It s my view that you might as well call the data invalid once you move off the magenta, because the unit has no way of predicting the next move. However, many pilots leave VNAV plugged in, using what would appear to be invalid data. This of course is verified when they update the LEGS page, and oops, all of a sudden we are 3000 feet low on profile.
The question is: How much lateral deviation will the FMC tolerate and still produce good data?
Does the FMC continue to calculate a profile based on a turn from PPS to the next waypoint, and if so out to what lateral displacement, before it throws up it's hands and says "can not compute"?
Thanks
Maui
Last edited by maui; 26th Dec 2012 at 10:00.