Originally Posted by
gums
We have returned to many discussions from the AF447 thread.
Oh gums, if only that were true. This particular back-and-forth has been going on since long before I joined this forum. I suspect, sadly, that it will continue for some time to come - as the subject acquired a political dimension very early on.
This requires knowing what the jet is doing versus what it's supposed to be doing, no matter what the "other guy" is doing. Any objections to that point of view?
Absolutely none, and I couldn't have put it better myself.
There should be a clear chain of command, and if the aircraft commander decides to take action, then it is mandatory to do so regardless of the rank or experience of the other guy.
History tells us that being too rigid here can bite us badly - I'm thinking of examples such as Tenerife in 1977, Birgenair 301, Palm 90... to name a few off the top of my head. I'd agree that the aircraft commander carries ultimate responsibility, and as such makes the final call - but only in split-second life-or-death scenarios should that call be unilateral, because your colleague may have spotted something you haven't. The book on QF32 shows Aussie-style CRM at its finest, and Capt. de Crespigny is not ashamed to admit that his first ideas were not always the best.
EDIT:
You do bring up some interesting points though, so let's have a look-see.
To the best of my knowledge the only airliner types still being used in significant numbers to retain a cable-to-surface connection (albeit for backup/manual reversion only) are the various B737 models, and the DC9/MDx0 derivatives. The design trend since the '70s seems to have been more in favour of engineering greater failsafes into the hydraulic system than cable-based reversion. This was unavoidable for widebodies, as the forces required to move flight surfaces of the required size are way beyond human muscle power. As to why this translated to narrowbodies, I can only speculate - but I do remember reading an interview with the Aloha 737 Captain who stated that flying the 737 in manual reversion almost completely exhausted him physically.
So it would seem that one benefit of beefing up the hydraulics means that the controls would behave in a manner to which the pilot is more accustomed. This is also the reason for the existence of Alternate Law. On the AF447 thread, people seemed to get bogged down in the minutae and making things seem more complicated than they are. There are three control laws in the Airbus system - Normal (which very few Airbus pilots will ever leave outside of a sim check), Alternate and Direct. There is only one Alternate Law, but it has various submodes depending on the type of failure that caused the degradation - the specific submode is largely academic, because the purpose of Alternate Law is ultimately very simple - and that is to work around the failures to provide as close to Normal Law behaviour as possible. Direct Law only engages in the air in the event of multiple serious systems failures - going back to the example of QF32, they were down to 50% of their electrical systems and 25% of the hydraulics with significant damage to the fuel system and holes in the starboard wing - even with all that, the control law they degraded to was still Alternate.