Egypt Air 990 767-300ER elevator split

[Frank_Rizzo]

Aside from the debate between US and Egypt over they FO crashed it on purpose I am interested in the elevator system that the reports really point out.

It is stated in the NTSBs report that when the captain came back after the initial abrubt movement that he told the FO and himself to simultaneously pull back/pitch up but the FO kept pushing forward/pitch down creating a split in the elevator control thus rendering a somewhat neutral effect at getting the plane back to level. Am I understanding correctly that each seat has completely independent control links to the elevator and there is no real overriding of either side eventhough the circumstance of intentional input split is rare. How consistant is this control split through the typical modern airliner fleet?

[fish314]

Originally Posted by Frank_Rizzo

Aside from the debate between US and Egypt over they FO crashed it on purpose I am interested in the elevator system that the reports really point out.

It is stated in the NTSBs report that when the captain came back after the initial abrubt movement that he told the FO and himself to simultaneously pull back/pitch up but the FO kept pushing forward/pitch down creating a split in the elevator control thus rendering a somewhat neutral effect at getting the plane back to level. Am I understanding correctly that each seat has completely independent control links to the elevator and there is no real overriding of either side eventhough the circumstance of intentional input split is rare. How consistant is this control split through the typical modern airliner fleet?

I'm not an expert by any means in the 76, but as I understand the system it was designed to work like this:

Both sets of controls work together and control both halves of the elevator in normal operations. The pilots controls were linked directly to one half of the elevator and the co's controls are linked to the other half. The two halves of the elevator are then connected to each other via a shear bolt.

The idea is that if everything is operating normally, everything is connected, and moving one yoke moves the entire elevator and the other yoke. It's all connected.

The whole point of that shear bolt, though is if something gets caught in the elevator and jams it. The idea being, if something gets physically stuck up there, then the pilot and co can each push or pull on the yoke, and that shear bolt will break. Hopefully, then one or the other side of the elevator would come free, and either the pilot's or the co's controls would be free to move and use the "un-stuck" half of the elevator to land the airplane.

As for how widespread the idea is, I have no idea. I used to fly KC-135's (which is basically a Boeing 707) and we didn't have anything like this.

[Cessnaflyer]

Originally Posted by fish314

The whole point of that shear bolt, though is if something gets caught in the elevator and jams it. The idea being, if something gets physically stuck up there, then the pilot and co can each push or pull on the yoke, and that shear bolt will break. Hopefully, then one or the other side of the elevator would come free, and either the pilot's or the co's controls would be free to move and use the "un-stuck" half of the elevator to land the airplane.

Wouldn't that create a huge rolling moment?

[fish314]

Originally Posted by Cessnaflyer

Wouldn't that create a huge rolling moment?

Well, it probably does create SOME rolling moment, but with the elevators as close to the centerline of the aircraft as they are, it's probably not very much.

Moment = Force X Distance, and if the distance is small there shouldn't be too much moment.

My guess is that it might be noticable, but not very difficult to compensate for using an aileron input. But that's just a guess.

[Frank_Rizzo]

Thanks for the responses!

[PositionAndHold]

Sorry I got to this late. I fly a Lear 45 and it has both, elevator and roll disconnect. I can't remember right now the exact mech linkage. Like what was said above, if we pull the ELEV DISC handle it splits the elevator, and the one that is not jammed we can use for control. If the ailerons get jammed, we can pull the ROLL DISC lever on the pilots yoke and use just the spoilerons for roll control.

[fish314]

Originally Posted by PositionAndHold

Sorry I got to this late. I fly a Lear 45 and it has both, elevator and roll disconnect. I can't remember right now the exact mech linkage. Like what was said above, if we pull the ELEV DISC handle it splits the elevator, and the one that is not jammed we can use for control. If the ailerons get jammed, we can pull the ROLL DISC lever on the pilots yoke and use just the spoilerons for roll control.

Have you ever tried it, maybe in the sim? Does the split elevator cause a noticable roll?

[Jason]

I've pulled the pitch and roll disconnects in the Challenger and CRJ (in the sim) and no - the roll moment wasn't even noticeable.