Suastiastu: noting the comparatively stable vertical speed (in terms of error band) that you point to, is it your idea that something new happened (maybe something broke) in the last half of a minute? When I look at the match up of the reported radio conversation between the aircraft and ATC as they were arranging their return, the impression I was left with was that the aircraft was more or less controllable, and then all of a sudden it wasn't.
This discussion takes me to a related incident that did not include a failure in the air (ILS Glide Slope gone bad) that has to do with
corporate culture and even
industry culture.
The previous crew who hand flew this bird back (whether or not they diagnosed the problem right) may have had a slightly different mind set, informed by company and industry culture, than the subsequent crew. In discussing the choice to hand fly the approach once the GS and the assisted approach has gone south, or to go around and try another approach, the following question is asked (in hindsight) for the recent approach that went around after their approach went unstable due G/S signal being bad.
Jet Jockey A4 : If you know there is a possible problem with the G/S signal and no other type of approach is available, why not hand fly the aircraft?
Capn Bloggs : You just never know when the technology is going to try to kill you!
Jet Jockey, you'll be put in the sinbin for suggesting that.
I am sure that discussions will continue regarding "why not turn it off and hand fly?" in this case, after the fact, but I note that crew in the bad ILS being discussed in the other thread didn't do that. (For my money, that close to the ground if things get unstable Go Around is something we were all taught in the beginning: no approach is too perfect that it can't be waved off ...)
How comfortable were these two pilots Lion Air with hand flying?
How comfortable were they with shutting systems off and flying the bird by hand? (The previous crew may have had a different comfort zone than the crew on this fateful day).
How much sim time, or flight time, did they have doing that hand flying thing?
Or, did something else break as the crew were dealing with "all this" and the investigators have not yet hit upon that failure as they go through their difficult and demanding tasks? I am reminded of the difference in the understanding of the AF 447 crash before and after the boxes, and their information, came to light.
We humans tend to do what we are comfortable with, though training can help us broaden our comfort zone. When the CVR is found, a lot of what I am wondering about in this accident will get answered, I think.