Originally Posted by
TTex600
FMC/FMS is not a fancy term for an advanced A/P, and they are not the exclusive domain for the "what's it doing now" problem.
FMS/FMC is the automation component regardless of FBW - "advanced A/P" (when compared to, say, the old Sperry and Smiths units) is as good an analogy as any.
I'm perfectly happy to be corrected by the way - can you name an incident where "what's it doing now"? was related to the FBW and not the automation?
BTW, why will my MCDU not accept the speed I program in it for a apeed/altitude crossing restriction? Sometimes it does, sometimes it doesn't. Why not? For example, a fix (jingl for example) must be crossed at 280 kts/17000ft but the FMC will not accept 280kts. I enter 280/17000, but it only gives me 275/17000.
I can't help you there I'm afraid - however there are many on here who can (I'd suggest A33z or rudderrudderrat).
Why will the 320 fly 260kts when the FCU is selected to 250kts in managed speed? (it's not a weight issue)
My guess would be an external factor in the managed flightpath - does it maintain 250 in selected mode?