Originally Posted by
GarageYears
It is still hard to understand why they didn't hit the trim cut out switches... The more I think about this, the more obvious that action seems.
- GY
Training. And the fact that you have had time to "think about this".
When I was on the Renton tractor (a few years ago now), the stab runaway event was trained by making the stab, er, run away. So it would, for some reason, go into a continuous clatter in one direction, which would do two things:
- Make the aircraft either climb or descend in an unwanted fashion, along with a cacophony of continuous trim wheel noise. It was all very obvious.
- The continuous noise (etc) would make you think: aha: stab trim runaway, and go for the switches.
This event is slightly different, and requires just 1 step of lateral thinking. Easily done here, but not so easy when all hell is breaking loose in the FD. There is no continuous clatter, so the training is not triggered. This is more "I just can't seem to get the thing in trim for pitch/power/etc, and I can't work out what's wrong". Being in a trim/thrust/pitch mess in a 737 is not uncommon (try a stall recovery using the old technique) and so the first thought is that you are once again in some kind of trim/thrust mess, rather than dealing with periodic unhelpful input from a genie in the trim system.
I have huge sympathy for these pilots, who I believe were confused by something they knew nothing about. The operator should not have dispatched, and the manufacturer should have disclosed the new system. I also have a suspicion that the sudden nose down is to do with the elevator breakout mechanism coming into play. But that's something for the specialists.