Bobbvis wrote:Having a hard time wrapping my head around trained pilots not being able to overcome a trim system malfunction to the point that it crashes the plane. The thumb switch is right there. If it keeps working against your wishes, reach down and turn it off. The Lion plane flew relatively straight and level for several minutes doing just that and then ???????? Why did they stop correcting it? This flight, I'm not sure we know enough, other than the jackscrew report, but maybe not enough altitude to counter the trim in time? Question- what kind of dive angle does full down trim produce? It's just trim isn't it? Fine adjustment? We're not talking dive bomber here are we?
If I recall correctly, the discussion was that, based on FDR control column force plots, that there was a change in which pilot was flying. When the SIC took over he did not trim nose up enough to counter the computer nose down trims. See below. The top line is the control column trim switch. Bottom line is the computer trimming. Middle line is stab angle. You can see for the first 6 or so minutes after they reach 5000 feet every computer trim down is countered by a control column trim up input of about equal time. And stab position stays roughly around 5 degrees. Then in the last minute or so, the control column inputs are very short, and the computer inputs eventually drive the stab to near full nose down