Narrative:

I am currently a captain on a B767, with absolutely no exposure to the B737 line. Therefore, I am not terribly informed on the most current theories involving the flight control problems involving the rudder. And likewise, I am not exposed to the latest techniques being taught by the various operators, should such a problem occur. However, in everything I've read concerning the B737 flight control problem, references are continually made to an uncommanded full rudder deflection, followed by aircraft yaw, roll and eventual upset. What I haven't seen is any mention of the pilot's attempt to reduce the thrust on the opposite engine to idle. I don't mean to oversimplify what is obviously a terribly complex problem, but in truth, that's why the rudder is there. For example, with an uncommanded deflection of the rudder to the left, perhaps reducing the right throttle would once again allow the crew to regain enough control to get the aircraft on the ground. Given the choice, I'm sure the pilots of the B737 that crashed would much rather have done a single engine approach and landing, no matter how compromised the rest of their flight control situation was. It's only a theory, and an untested one, at that. Even if it works, it certainly won't solve the rudder problem in the B737, but it just might help a crew survive the next time it happens. Callback conversation with reporter revealed the following information: the reporter said that he has talked to his company's training department and his chief pilot and they were receptive to his suggestions about using differential to recover from an uncommanded roll type of upset. The training department is going to test the technique in the simulator and determine if it can be taught as a secondary recovery technique. The captain said that his thoughts on the subject of using differential thrust were to use this if all else failed to right the aircraft during an uncommanded roll. He believes that if the crew had already attempted to use the rudder and ailerons to no avail or, at most, an incomplete recovery than differential thrust may allow a complete recovery. He is not promoting this as a primary technique or a sole use technique.

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Original NASA ASRS Text

Title: A CAPT SUGGESTS THAT USE OF DIFFERENTIAL THRUST MAY ASSIST B737 CREWS TO RECOVER FROM UPSETS CAUSED BY UNCOMMANDED RUDDER DISPLACEMENTS.

Narrative: I AM CURRENTLY A CAPT ON A B767, WITH ABSOLUTELY NO EXPOSURE TO THE B737 LINE. THEREFORE, I AM NOT TERRIBLY INFORMED ON THE MOST CURRENT THEORIES INVOLVING THE FLT CTL PROBS INVOLVING THE RUDDER. AND LIKEWISE, I AM NOT EXPOSED TO THE LATEST TECHNIQUES BEING TAUGHT BY THE VARIOUS OPERATORS, SHOULD SUCH A PROB OCCUR. HOWEVER, IN EVERYTHING I'VE READ CONCERNING THE B737 FLT CTL PROB, REFS ARE CONTINUALLY MADE TO AN UNCOMMANDED FULL RUDDER DEFLECTION, FOLLOWED BY ACFT YAW, ROLL AND EVENTUAL UPSET. WHAT I HAVEN'T SEEN IS ANY MENTION OF THE PLT'S ATTEMPT TO REDUCE THE THRUST ON THE OPPOSITE ENG TO IDLE. I DON'T MEAN TO OVERSIMPLIFY WHAT IS OBVIOUSLY A TERRIBLY COMPLEX PROB, BUT IN TRUTH, THAT'S WHY THE RUDDER IS THERE. FOR EXAMPLE, WITH AN UNCOMMANDED DEFLECTION OF THE RUDDER TO THE L, PERHAPS REDUCING THE R THROTTLE WOULD ONCE AGAIN ALLOW THE CREW TO REGAIN ENOUGH CTL TO GET THE ACFT ON THE GND. GIVEN THE CHOICE, I'M SURE THE PLTS OF THE B737 THAT CRASHED WOULD MUCH RATHER HAVE DONE A SINGLE ENG APCH AND LNDG, NO MATTER HOW COMPROMISED THE REST OF THEIR FLT CTL SIT WAS. IT'S ONLY A THEORY, AND AN UNTESTED ONE, AT THAT. EVEN IF IT WORKS, IT CERTAINLY WON'T SOLVE THE RUDDER PROB IN THE B737, BUT IT JUST MIGHT HELP A CREW SURVIVE THE NEXT TIME IT HAPPENS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID THAT HE HAS TALKED TO HIS COMPANY'S TRAINING DEPT AND HIS CHIEF PLT AND THEY WERE RECEPTIVE TO HIS SUGGESTIONS ABOUT USING DIFFERENTIAL TO RECOVER FROM AN UNCOMMANDED ROLL TYPE OF UPSET. THE TRAINING DEPT IS GOING TO TEST THE TECHNIQUE IN THE SIMULATOR AND DETERMINE IF IT CAN BE TAUGHT AS A SECONDARY RECOVERY TECHNIQUE. THE CAPT SAID THAT HIS THOUGHTS ON THE SUBJECT OF USING DIFFERENTIAL THRUST WERE TO USE THIS IF ALL ELSE FAILED TO RIGHT THE ACFT DURING AN UNCOMMANDED ROLL. HE BELIEVES THAT IF THE CREW HAD ALREADY ATTEMPTED TO USE THE RUDDER AND AILERONS TO NO AVAIL OR, AT MOST, AN INCOMPLETE RECOVERY THAN DIFFERENTIAL THRUST MAY ALLOW A COMPLETE RECOVERY. HE IS NOT PROMOTING THIS AS A PRIMARY TECHNIQUE OR A SOLE USE TECHNIQUE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.