Comment by sillysaurusx | Hacker News Reader

Comment by sillysaurusx | Hacker News Reader

Parent Full thread

Yes, but I'm not sure why it inverted. If you open the accident report (https://www.ntsb.gov/investigations/AccidentReports/Reports/...) and ctrl-F "rudder", you get 2,112 matches. So "reading for hours" is a distinct possibility in this case...

(Oh, by the way, I didn't mean to imply you were mistaken, or anything like that. I was just so shocked that a plane's controls could invert themselves in any conceivable circumstance. Currently digging through the accident report to try to figure out what happened.)

"the probable cause of the USAir flight 427 accident was a loss of control of the airplane resulting from the movement of the rudder surface to its blowdown limit. The rudder surface most likely deflected in a direction opposite to that commanded by the pilots as a result of a jam of the main rudder power control unit servo valve secondary slide to the servo valve housing offset from its neutral position and overtravel of the primary slide"

Unfortunately I don't know what most of these terms mean. It sounds like it might be saying "they moved the rudder to its limit, and then it jammed at the limit; so when they tried to command the rudder to go the other way, the rudder was pointed in the opposite direction of the control inputs." But I'm really not sure.

No offense taken. I meant that if I start researching it again I’ll be up for 5 hours because of the personal ties to it.

My recollection in researching this a decade ago was that the cold weather made the behavior of the rudder change (my term was invert, maybe that’s not accurate), and pilots were trying to pull up, but in fact putting the plane deeper into a nosedive. Some 25 seconds later they hit the ground at some 300-400 MPH and vaporized.

The only way to have saved the plane would have been to dump the hydraulics and/or switch to a manual fly by wire mode, neither of which were a logici thing to do in the 15 seconds they had to save the flight.

I’ve only flown for 20 hours in a Cessna so sorry if my terminology isn’t perfect!

> ... behavior of the rudder change (my term was invert, maybe that’s not accurate), and pilots were trying to pull up, but in fact putting the plane deeper into a nosedive.

The rudder controls yaw, not pitch. The rudder controls did invert: the pilot tries to turn slightly left, the plane turns right, so the pilot naturally tries turning harder left until the rudder is in the full right position, and they're in an uncoordinated turn. The wing on the inside of the turn starts to drop significantly or even stalls. The plane is then sideways and in a dive, and on top of that, the rudder is all the way over in the direction that makes the dive steeper. The planes quickly rolled over on their sides and went into steep dives.

My understanding is that a big break in the case came when a pilot figured out what was going on and successfully landed a plane with reversed rudder controls.

Reply on news.ycombinator.com