Originally Posted by
Goldenrivett
I disagree. The aircraft trimmed full nose up in response to the co-pilot's continuous back stick demand for more nose up.
One of the holes in the cheese could have been closed with active side sticks so that the other pilot may have recognised the gross handling error of constantly pulling back.
Active sidestick is not something new, Airbus could have coupled both side sticks easily, however it added some weight so I assume that was the main reason why they did not do it.
Yes, holding full back stick without a good reason and with no protection is stupid, but accompanying/encouraging/amplifying a stupid movement is stupid too, isn't it ?
Actually, there are two other important examples that show the error in Airbus design :
- The MCAS accidents (from Boeing) showed that uncommanded/uncommandable/hidden/insufficiently visible trim runaway is dangerous, but Airbus too is capable of surprising trim runaways.
(Actually, since Airbus hides in fact the entire THS from the pilot, if the pilot is made aware of a THS movement it is necessarily a surprise)
- The XL airways crash at perpignan showed the sheer danger of a fully upwards THS. Even with full down stick, they could not impose the correct trajectory on the aircraft.
Instead, the aircraft imposed them with a deadly climb up to more than 50° nose up pitch.
The THS, or more generally pitch trim, should only relieve the efforts on the stick. A correctly designed aircraft should (that's only my opinion as a pilot) always be controllable with a trim completely ran away in the wrong direction. And if that's not possible by the law of physics (as seems to be the case of the airbus) there should be serious measures to prevent this type of accidents :
- The THS cannot move to an area where the airplane won't be controllable in an automatic/hidden fashion, or
- The THS should revert automatically to a desirable position when the pilot applies large stick inputs that cannot be satisfied by the elevators only.
To me, this sounds like common sense.
Hold full back-stick, or yoke in any aircraft, and it will stall. Keep holding full pitch-up during the stall and descent, and you will crash. The standard stall recovery is to immediately pitch down - this should be instinctive to experienced airline pilots.
In the case of the XL airways crash, they applied full pitch down and would have been able to recover the aircraft in this dire situation, if only airbus had not trimmed itself automatically fully up.
Try to answer this question positively : is there any good reason to allow the THS to go fully upwards or fully downwards, in a way that will make the aircraft uncontrollable ?
Is there any good reason to allow the THS to go automatically and unknowingly outside of a safe zone that could be computed from the current CofG ?