Originally Posted by ExV238
With great respect, have you flown an Airbus in Alternate Law? At high altitude?
The transition is seamless, and roll control is not so different to Normal Law. with regard to your first sentence above, I wonder how many pilots have actually manoeuvred their aircraft in Normal Law at cruise alts? Not many, I bet. And even fewer would have used full deflection roll inputs under those conditions, which gives 15 degrees per second in Normal Law in the Airbus. I believe that the issue is general unfamiliarity with high altitude/high Mach manual flying and reations to upsets than it is about 'degraded' flight controls.
ExV238, I'm just one of the guys, and I don't take offense easily so do not worry about an adverse reaction. Just speak your piece and don't hold back.
First, to be absolutely clear, I am a tactical jet pilot by experience and at heart. The closest I came to multi-pilot transport operations was flying the Navy C-1A transport on logistic runs and cross countries at a couple of duty stations. But before you think, "just another keyboard commando," you might wish to take into account my experiences and historical perspective on aviation.
Unlike most of those here who are flying the line, I have had some experience with roll PIO and those few seconds of PIO were so gut-wrenching that I remember them clearly to this day. This was in a visual simulator no less! Can you perhaps imagine the sensation of the poor souls flying AF447/QZ8501 who understood that "This is for real and it is all on me to save the day?"
. One of the things about AF447 that stands out was the initial roll oscillation that lasted for 30 seconds or so. Everyone looking at the data was saying it wasn't that bad of an oscillation and he got it under control in 30 seconds. But if your were looking at the data from the inside view, I could see clear signs that the pilot had to develop a strategy to attempt to control the roll oscillation and that this strategy had actually prolonged the oscillation. (He was attempting to get ahead of the oscillation by accelerating his roll inputs.)
This fits the definition of a PIO. If it had not been a PIO, he should have been able to stop the oscillation immediately.
On QZ8501, the aircraft got to 54 degrees bank angle before the roll correction was applied. In addition, the FAC system is responsible for re-configuring the PFD airspeed display for Alternate Law but the FACs were disabled. I expect the only place he might have quickly seen that he was in Alternate Law was on the ECAM display.
A strong roll input was applied and the aircraft reached 6 degrees of bank in less than 2 seconds before it reversed and reached almost the same initial bank. FCOM states that in roll direct in a clean configuration, the maximum roll rate is about 30 degrees per second. When you consider that the roll rate had to be decelerated to reverse, it is clear that peak roll rates were easily in the maximum range. In hands of an inexperienced pilot in cruise flight, this type behavior should be looked at as roll PIO until proven otherwise.
With regard to the concept of a seamless transition from Normal to Alternate, think back to your initial training on Alternate Law. Weren't you first briefed on it and told to be gentle with the controls? Then you had a clear transition to Alternate Law, and after about 15 seconds, you had the feel for it and afterwards it was no big deal. Contrast that introduction with what the pilots flying AF447 and QZ8501 received. No warning, no briefing, no previous experience, a confusing transition to Alternate Law with other factors in play, and then a hurry up and try to catch up with an aircraft that is rolling. No wonder they over-controlled.!
Now for the Boeing guys here, this is primarily an Airbus training and probably a design problem as well. Something that Airbus would rather not be addressing under time constraints. But don't let your guard down. I can post a video of a triple 7 doing a roll PIO on short final and into the touchdown if you need motivation.
Gums, thank you for your recent input.
The gents suggesting a stick shaker for the Airbus have it right. The sooner the better.
But there is a lot that can be done to make the transition to Alternate Law uneventful.
