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Yes. This took a long time to work out with initial finger pointing between Boeing and the Pilot unions. "Testing revealed that under certain circumstances, th
by throwaway201103 6y ago
Yes. This took a long time to work out with initial finger pointing between Boeing and the Pilot unions.
"Testing revealed that under certain circumstances, the Power Control Unit (PCU)'s dual servo valve could jam and deflect the rudder in the opposite direction of the pilots' input. Thermal shock testing revealed that the uncommanded rudder movement could be replicated by injecting a cold PCU with hot hydraulic fluid. Thermal shock resulted in the servo's secondary slide becoming jammed against the servo housing, and that when the secondary slide was jammed the primary slide could move to a position that resulted in rudder movement opposite of the pilot's commands"
https://en.wikipedia.org/wiki/Boeing_737_rudder_issues https://en.wikipedia.org/wiki/Boeing_737_rudder_issues
- sillysaurusx 6y agoresulted in rudder movement opposite of the pilot's commands Did the rudder actually move in opposition to the commands, or was it stuck at some limit value? i.e. in that situation, if you command the rudder to go left, does it move even more in the wrong direction? Or is it simply frozen at whatever position it happened to get stuck in? Thanks for the info!
- throwaway201103 6y agoI'm not sure. I'm not a pilot and only have memory of this from prior reading. As I look at it now it reads more like it was uncommanded movement to the limit of travel and getting stuck there. I've also heard this problem referred to as the "rudder hard-over" problem. But there are also statements about rudder movement opposite of that commanded. In theory the problem was recoverable but the pilots had about 10 seconds to realize what was going on and react appropriately. Sounds familiar to the 737-MAX uncommanded trim issues.