I agree with PJ2 about his analysis of the crew reactions and our discussions about control law reversion, as well as the function of the THS.
The thing that bothers me is the lack of "feel" that the system provides to the pilot. I fully understand the Nz law, which seems to me primary for the 'bus, and corrected for pitch attitude with little regard for AoA. That's important - corrected for attitude.
So you don't really have a one gee command if not fairly close to zero pitch attitude. Hence, HAL is trying to achieve 0.87 gee at a 30 degree pitch attitude, and less if you figure the sine/cosine/etc .
The big deal with the THS is that it is trying to relieve the required stick pressure/displacement if the pilot is holding a command other than the one gee corrected for pitch attitude. For a commercial airliner, this makes perfect sense to this dinosaur.
The problem is that simply releasing pressure/displacement does not give you the "feel" that we used to have when the basic aero of the jet tried to achieve a trimmed AoA. In other words, going too fast or pulling too hard, the jet would try to go back to the trimmed AoA/gee if we relaxed the pressure/displacement ( NOTE: Our primitive FBW implementation used pressure , not stick displacement, so simply relaxing pressure would command the jet to go back to the trimmed gee). . So the THS concept seems to get in the way of what we old farts "felt" when we were commanding something that the jet was not trimmed for. Does this make sense?
The Boeing FBW implementation appears to use a mechanical "artificial feel" that requires ever-increasing pressure/movement to maintain other than trimmed gee/AoA. I don't see this on the 'bus.
My opinion after these last three years of discussion and analysis of the 'bus flight control laws leads me to this :
- The jet performed exactly as designed.
- The THS logic and lack of increasing stick pressure to command an unusual pitch attitude/AoA "helped" to maintain a condition that made a recovery very difficult for the average or even above average pilot that had not thought this scenario through. The 'bus has postitive longitudinal stability thoughout it's envelope unless the fuel trim system is completely FUBAR. So the jet would appear to act as we old folks would expect in the so-called "direct law". Unfortunately, the system keeps trying to achieve a gee-command ( corrected for pitch attitude) and there's no obvious indication/feeling via the stick that the plane wants to achieve an AoA versus a gee.
- The AoA inputs to the flight control logic should be emphasized more IMHO, and good AoA sensors work well down to 50 or 60 knots of actual dynamic pressure, regardless of what the pitot-static system(s) is telling the system.
- Crew coordination and a clear "chain of command" is essential if you are flying a "crewed" airplane that allows more than one pilot to have a control input. My only experience in "crewed" planes was as an instructor in a family model of two jets ( ultimate authority!) or in the VooDoo, which had a radar operator in the back seat with no flight control inputs. So I defer to those here who have thousands of hours dealing with the "CRM" issue. All I ever had to do was ask, "Gums? What the hell are you doing?"