Originally Posted by
flyingchanges
. B737 trim does not work the same as small aircraft trim. In small aircraft you trim out the forces. But in B737 which has THS, you do not necessarily trim out the force. As a matter of fact, you can have the control column in neutral position with no force, while the THS is being trimmed hard forward and not feel anything on control column.
Actually to some degree, this is true. You still trim out the control column forces, but for the most part, the yoke remains centered when trimmed. In a light ac, you are changing the position of the elevator and yoke with trim changes.
Firstly, not all light aircraft are the same. The trimmer on a Piper Cub is exactly the same as the 737. And yes, the stick or cc will remain in the same place as you trim forwards, but unless you give a mighty pull on the stick or cc, the aircraft is going south very quickly. So you cannot trim without experiencing stick or cc forces.
And regards this incident, I cannot see anyone trimming forward without noticing the loud racket from the antique trim system, or the sudden pitch down, or the large cc forces required to resist this. The only thing that might make sense is a trim runnaway, that was not caught in time. Remember that if the flaps were still extended, the trim runs at double the rate. Not sure why it would not be stopped, as it is easy to hear and see, opposite cc pressure should stop it, and you can grab it with your hand if you don't mind losing a finger.
The mystery remains. The only thing we can perhaps dismiss, is a stall or a Bournemouth thrust pitch, as the VS, altitude and GS plots don't support these scenarios.