Non-Stoppable Stabilizer Trim Runaway

[United744]

Hi,

A friend and I were flying in multi-crew config last night, and for fun my friend started throwing failures at me (I was PF). It largely went OK  :lol:  except I noticed a strange behavior after he failed the stab trim.

The aircraft initially started a slow, uncommanded pitch up which was quickly identified, and so I set both stab trim switches to CUTOFF. The aircraft eventually required full nose down elevator to stop the pitch increasing any further.

At first it appeared the aircraft was in some kind of control, but for reasons unknown, it then would suddenly start pitching up from a steady state. This resulted in me applying full roll input to stop the climb, and to get the nose down (aircraft was rolled about 80 degrees to one side through the maneuver). Once the nose started to drop, I rolled the aircraft up the right way. Again, the aircraft then appeared to be under control, when a moment later it would do it again.

At this point I requested the flight controls to be displayed on the lower EICAS so we could better see what was happening. At the moment of the pitch up, the elevator inexplicably went to neutral, requiring the elevator input to be changed to put it back to the full nose down position. Once we realized this was occurring, the aircraft was largely controllable, and made a survivable landing.

Why would the elevator suddenly reset to neutral, whilst the stick is being held forwards?

We were flying with Beta 2.

[Hardy Heinlin]

Hi,

the joystick of the one user was shaking in the neutral area, overriding the other user's joystick which was steady at max deflection.

The last shaker wins.

The last word is always the last word.


Cheers,

|-|ardy

[United744]

Ahh! That would explain it. Thanks!