Originally Posted by
Machinbird
Since the turnover briefing specifically included the discussion about the aircraft not being ready to climb higher, there are approximately two reasons the aircraft would be put in a climb.
- PF airspeed indication approaching Mmo or
- It was inadvertent.
I would perhaps also add "they lost attitude indications and thought they were diving" (somatogravic illusion etc.)
I think it is low probability, but PF displays aren't in the flight data, and there is the line in the BEA release:
PF said "I don’t have any more indications", and the PNF said "we have no valid indications".
As well as the comment itself, I find it interesting that the BEA chose to include it in this early release. We have what is surely just secleted excerpts of the CVR transcript at this point, so why did they include this line ? Do they already believe it is significant ?
Did the pilots
lose attitude info, or did they
distrust attitude info, or ? Climb might therefore
possibly have been deliberate ? [ I know the climb happens before this comment, but the comment could be on a failure (or not) that happened earlier ].
Large control inputs (high gain activity for the control theorists) are contrary to this Pilots training. Something scared the Bejesus out of him to get this type of behavior.
The only thing that makes sense is that he encountered lateral PIO (And PIO is definitely an aircraft problem).
Another name for PIO is pilot in the loop oscillation.
Entirely possible, and I've been wondering about it too.
Inspired by Gums' great posts on the Viper FBW (further back than my small knowledge of it, and fascinating history) I did some digging for info on that, and one thing that came up was this paper on PIO:
http://www.nasa.gov/centers/dryden/p...ain_H-2031.pdf - looks like just putting the g-forces on the pilot's arm into the loop can get you interesting results in certain conditions. I doubt that is what happened here, but it gives an insight into the complexity of the overall model and what it can throw up. [ Note: for the anti-FBW brigade - PIO is
not a consequence of FBW, and modelling the overall control system for direct cable control would be at least as complicated, and likely much more so ].