Originally Posted by
Machinbird
Maybe we will learn something Friday regarding how different FBW is.
Here is some "homework" for those who wish to get their minds ready to understand a bit more about what makes FBW different.
Fly-By-Wire A Primer for Aviation Accident Investigators
The quiz question is: How does the pitch feedback in the A320 at 180 knots differ from that at 230 knots?
Trick question ? Is that 180 indicated and 180 actual, or 180 indicated and 230 actual ? The latter would be different again if only because the aerodynamic response would change, no ?
There is also the question of what the FBW uses to calculate gain in the event of unrelaible airspeed - last-known-good value (which might be wrong...) or fixed mid-value or some other calculated value ? I doubt it uses known-bad data, so if you do have 180-indicated at 230-real, that doesn't mean you'll get the gain set to the normal value used at 180. Am I on the right track ?
A page or so back in the thread, someone posted on an airline investigation showing pitot issues -> unreliable airspeed on one in 80k flights (!) - by my reckoning that's a
lot of issues over the years worldwide (even if only Thales equipped buses) , far more than just the other events listed in the reports, yet without planes falling out of the sky.
So on that track, the answer to "How does the pitch feedback differ" would be: not by enough to cause a serious problem if the speed indication is wrong. Until 447. Something different to all the other cases happened on this flight, what, we don't know yet (maybe the VS really did fall off
). Tomorrow we may know.