Originally Posted by
TTex600
You're incorrect and I've already given the reason. An FMC/FMS is not an advanced autopilot.
You've yet to tell me *why* though - it'd be very helpful!
If you want to discuss in context, 'll be glad to do so. Actually, I'll help you - again. The context was this: pilots do not always know exactly what an airplane is doing. Go back and read post 649 from the "AF447 Report Out" thread Rumours and News. Here, I'll make it easy for you
Thanks - OK.
So, my position - which happens to be fact - is that FBW is not automation. Never has been. FBW relates purely to the link between the control inputs (whether they be manual or automatic) being digital in nature and being passed through a computer, rather than through electro-mechanical or pure mechanical means - to the flight surface actuators.
To my knowledge, the "what's it doing now?" incidents (i.e where "pilots do not always know exactly what an airplane is doing") are FMC/FMS rather than FBW-related. If you disconnect the FMC/FMS and fly an A320 manually, the computer will do everything you ask of it - up until the point where alpha max is reached or the G loading exceeds the level where structural damage is likely.
The only instance of a grey area that I can think of was the Habsheim crash, where it was not so much a case of "what's it doing now?" as "why won't it give me more nose-up?". The answer to that question was "because if it did, you'd have stalled - and you disabled autothrust so alpha-floor can't help you".
So - as to your earlier point:
Originally Posted by
TTex600
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.
Why will the 320 fly 260kts when the FCU is selected to 250kts in managed speed? (it's not a weight issue)
These are questions relating purely to automation - FBW doesn't come into it.
We could probably get along well if you could find it in yourself to answer what I write instead of trying to use my words tomorrow further your jihad against what you judge to be misinformation.
Believe me I'm trying my best - it does none of us any good to be combative!
I'm just trying to set a baseline for discussion based on what I know and that is that FBW and FMC are completely separate and distinct systems.
Regarding the questions I asked. I know the answers......because.......... I actually operate the airplane.
I'd be really happy to know - do tell!
Originally Posted by
wozzo
So you know the answers, but you won't tell us, because Doze was mean to you?
Mean? I've never been anything less than honest, enthusiastic and hungry for information! If I've come across as mean at any point, please accept my humble apologies...
Originally Posted by
CONF iture
That specific item is a flight control in a stall scenario.
As I said before, the flight control computers have no concept of "stall". They "know" about alpha max, however. In Alternate Law the computers allow a pilot to exceed alpha max (as well as the load limits) if sufficient control force is applied.
Come on - you're well-read on Habsheim. When the Captain tried to pull past alpha-max the computers didn't simply disregard the pitch command, they held the aircraft just shy of alpha-max, including ND elevator commands where necessary. The reason for this is that the hard protections aren't part of the system which controls the surfaces, they are a separate system that monitors the aircraft's position relative to those limits and will maintain those limits until such a time as the command in the opposite direction is given.
Think of it as a bounding cuboid around the aircraft, constantly changing in dimension based on the aircraft's pitch, bank, AoA and speed data. In Normal Law, there isn't a bit of logic that says "Don't move THS/elevator/aileron beyond this position" - the logic says "if these limits are reached or exceeded, use all the flight controls to remain stable at this limit". A drop from Normal Law to Alternate 1 replaces the "do not exceed" logic with "return to this limit when controls are released". A drop to Alternate 2 and beyond removes it entirely.