Originally Posted by
Uplinker
Ah. Yes, modern autopilots and FBW* are so good that one sometimes gets a nasty surprise on disconnecting to land!
(* Airbus, I don't know about Boeings - I am sure they are just as good)
The disadvantage of Airbus FBW is that in Normal Law there is no feed back through the side stick to tell you how much aileron / elevator is being applied.
See accident report of the Hamburg incident
http://www.bfu-web.de/EN/Publication...ublicationFile Summary Siet 12.
"When the respective ELAC unit has detected that the aircraft has touched down, within 0.5 seconds the system changes from Lateral Flight Law to Lateral Ground Law. The effect of this is:
• to cancel the aircraft feedbacks used in flight for the computation of ailerons / spoilers deflection, this one being only made using sidestick orders information,
• to limit the ailerons and roll spoilers 2, 3 and 4 deflection by about a half at high speed (Vc > 80 kt)”
When you disengage the AP and are manually flying in Normal Law, you still have no idea what the control surfaces are actually doing to satisfy your inputs. In gusty conditions, a small roll rate request on the side stick may need full aileron displacement - and you won't know.
How many qualified A320 pilots know that you only can get half aileron deflection with full side stick on landing?
See:
Near-Crash in Hamburg: Investigators Criticize Airbus for Inadequate Pilot Manuals - SPIEGEL ONLINE