I reported yesterday about an All Nippon Airways Boeing 737 that went out of control after its co-pilot mistook a flight control for a doorknob. Patrick Smith, writing at Slate, has more information about that incident.
I can’t say for certain what happened, but presumably it went something like this:
There in the cockpit in the dark of night, the first officer reached for what he thought was the door release, inadvertently depressing the rudder trim switch. He held the lever down; the door did not open. So he held it down some more.
The rudder trim is a device that electrically fine-tunes the force applied to the plane’s rudder — the movable surface attached to the tail that helps control the side-to-side “yaw” motion of the airplane. You don’t use it all that often, and when you do, it’s a momentary push. The longer the pilot held this switch, the more pressure he was applying, a little bit at a time, and the more the plane wanted to twist to one side. It would have been easy for this to go unnoticed because the autopilot was engaged, and the trim commands would not have been evident until suddenly the autopilot couldn’t handle them anymore and disconnected. All of this takes place over several seconds.
At this point there was still enough time to avoid the upset. And that’s the real issue here: why and how the plane got away, not the button-pressing itself. We suppose the the pilot was caught by surprise and did not understand what was happening until it was too late. Add to the scenario the fact that it was nighttime. Almost anything that can go wrong in a cockpit is more challenging under darkness than in daylight.
. . .
Nervous fliers, look on the bright side: The video helps demonstrate how a 737 can safely endure even highly extreme upsets, and should remind you that even the worst turbulence doesn’t come close to exceeding the structural limits of the aircraft.
There's more at the link.
Mr. Smith's regular column at Slate, 'Ask The Pilot', appears to be interesting and entertaining reading. I'll be going back there to read through his archives.