Originally Posted by
Machinbird
That would be in Mechanical Law. The last ditch bring it back mode of control.
True, but it is possible to use the trim manually in any law. Manual Trim has priority, and when manual trim commands cease, autotrim will function again. I misinterpreted that earler, thinking that manual trim activation was a one-shot action which disabled autotrim for the duration. That said, if the pilot doesn't like what autotrim is doing all he or she has to do is keep their hand on that trim wheel.
Originally Posted by
Smilin_Ed
Ascribing some of the blame to the pilots will not get Airbus/AF off the hook.
Agreed. I think we're on the same page
From a pilot's perspective, if someone hands me the controls and says "You have it." I want him to keep his hands off until I hand it back to him. I don't want him to touch the trim unless I ask him to do so. Maybe not all pilots agree with that but I was trained to evaluate the "Flying Qualities" of aircraft. I made my living doing just that and my opinion is that the autotrim needs to come out when the confusers get thoroughly confused and give up trying to fly the aircraft.
That's a good point, and I'm sure that will be taken into consideration. Having said that I think your use of "confusers", while amusing, is an example of the adversarial attitude I was talking about earlier and undermines the very salient information you provided above.
@Dozy: Yes, the ability to manually control the trim is there but they didn't use it. We don't yet know why but it is clear that they let the system trim them up into a stall. In the world of pilots, that is a big no no.
@Dozy: But, in this case, the system did hinder the pilots. The pilots were remiss in not catching the fact that trim had run full nose up, but the system put it there when it shouldn't have, reducing their ability to fly it out of the stall.
Now this is the point when things get tricky. What you perceive as "the system" trimming them into a stall could equally accurately be described as the PF inadvertently trimming them into the stall by his direct actions, if indeed it turns out that the THS movement was sidestick-induced.
This is why I try to be really careful with language here because I don't want to give anyone the impression that I'm disrespecting the piloting profession when nothing could be further from the truth. We all make mistakes in our day-to-day lives, some of which have more far-reaching consequences than others. Being in charge of a two hundred-ton metal tube moving through the sky just below the speed of sound with a couple of hundred people behind you means that for line pilots, those consequences tend to be more far-reaching on an almost constant basis. When I hear the phrases "I don't believe a pilot would do that", "No pilot in his right mind would do that" or "A pilot would never do that" I get a sinking feeling (with no instruments to reference to confirm my physical perception
). This is because we're all human, and pilots - some of whom were below average, but many of whom were experienced, skilled and respected - have nevertheless done things like attempting a take-off without clearance/in snow conditions with engine anti-ice off/with high-lift devices not extended, shut down a working engine leaving the aircraft to fly on the damaged one, pulled back on the control column turning a stall warning into a full stall... the list is a long and sad one.
To be clear, I'm not bashing pilots here - I'm simply stating that the consequences that the men and women of the piloting world face for the kind of momentary lapse in judgement that would be easily resolved in almost any other workplace are far more severe, and that's why I personally have a lot of respect for all of you. But being almost hair-trigger defensive in the way that I see sometimes on here does you a disservice, when what I'm sure engineers all want is to make your (and our) lives as easy and safe as we can.
Right now we're speculating on information that was barely more than a press release. The people that designed these systems weren't stupid, and I'm sure there are very logical reasons for the system being designed the way it is. Remember that this was designed to be the next generation of flight controls - doing things a certain way because that was the way they'd been done since WW2 (or even beforehand!) wasn't a valid design input. Being as friendly and logical to the pilot as possible certainly was, the only problem with that being that some pilots prefer different things.
In every fixed wing aircraft that I have flown, directional stability and pitch stability are positive and only lateral stability is neutral. The Wright brothers initially thought that they wanted neutral pitch stability but after a couple of flights, they began to realize that pitch stability had to also be positive. If not, when they pulled the nose up, it would stay there until the aircraft stalled. That's when they changed their design to positive pitch stability which brought the nose back to the trim speed when they let go of the controls. Having the autotrim follow the sidestick commands essentially gives the aircraft neutral pitch stability. Neutral pitch stability is fine as long as the autopilot is functioning properly, but when it quits, you really need it to be positive when you are hand flying.
I'd need someone like PJ2 or Chris Scott to provide the data, but I'd be very surprised if they didn't factor that basic aeronautical knowledge into the design somehow (I'm a logic guy, the complex maths isn't my forte). We're not going to know exactly what the inputs were until the report is released, so I think we're going to need to keep our powder dry until then.