Narrative:

Encountered wake turbulence at 2000 ft behind a B-737 4 mi ahead. We were at 200 KIAS, 2000 ft, flaps going to position 5, autoplt off, when we entered preceding B-737's vortices. Our B-737 first felt like light turbulence, then right wing dropped quickly. I used rudder and yoke to bring wing back to level, then wing dropped to the left before I could again pick it up with rudder and yoke. Plane continued to roll, yaw, and heave for 10 seconds or so. We were trapped inside a vortex, not just transitory. Estimate wing drops of around 25 degrees left and right. Had we been in autoplt control I believe the aircraft would have gone past 90 degrees wing down. B-737 autoplts don't have rudder authority/authorized -- only the pilot does. In wake turbulence, disconnect the autoplt and fly the jet! Callback conversation with reporter revealed the following information: reporter has very positive ideas regarding use of autoplt on approach. He feels strongly that one should be prepared to click it off immediately if aircraft gives any adverse indications of uncontrolled input or forces. Most autoplts take 8 seconds to kick off on their own if motion is beyond autoplt capability. That is too long in such a situation as this. The autoplt does not use rudder input to make corrections and that is precisely what was needed in this incident to regain control. Reporter's company is about to install HUD and this will require a hand flown aircraft on approach. He feels this will be a much better approach. Reporter called his chief pilot as he is a member of the safety committee and wanted to pull the flight data recorder. Reporter was in the process of writing a safety article on wake turbulence and got first hand knowledge for the article.

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Original NASA ASRS Text

Title: 737 EXPERIENCES WAKE TURB FOLLOWING ANOTHER 737.

Narrative: ENCOUNTERED WAKE TURB AT 2000 FT BEHIND A B-737 4 MI AHEAD. WE WERE AT 200 KIAS, 2000 FT, FLAPS GOING TO POS 5, AUTOPLT OFF, WHEN WE ENTERED PRECEDING B-737'S VORTICES. OUR B-737 FIRST FELT LIKE LIGHT TURB, THEN R WING DROPPED QUICKLY. I USED RUDDER AND YOKE TO BRING WING BACK TO LEVEL, THEN WING DROPPED TO THE L BEFORE I COULD AGAIN PICK IT UP WITH RUDDER AND YOKE. PLANE CONTINUED TO ROLL, YAW, AND HEAVE FOR 10 SECONDS OR SO. WE WERE TRAPPED INSIDE A VORTEX, NOT JUST TRANSITORY. ESTIMATE WING DROPS OF AROUND 25 DEGS L AND R. HAD WE BEEN IN AUTOPLT CTL I BELIEVE THE ACFT WOULD HAVE GONE PAST 90 DEGS WING DOWN. B-737 AUTOPLTS DON'T HAVE RUDDER AUTH -- ONLY THE PLT DOES. IN WAKE TURB, DISCONNECT THE AUTOPLT AND FLY THE JET! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR HAS VERY POSITIVE IDEAS REGARDING USE OF AUTOPLT ON APCH. HE FEELS STRONGLY THAT ONE SHOULD BE PREPARED TO CLICK IT OFF IMMEDIATELY IF ACFT GIVES ANY ADVERSE INDICATIONS OF UNCTLED INPUT OR FORCES. MOST AUTOPLTS TAKE 8 SECONDS TO KICK OFF ON THEIR OWN IF MOTION IS BEYOND AUTOPLT CAPABILITY. THAT IS TOO LONG IN SUCH A SIT AS THIS. THE AUTOPLT DOES NOT USE RUDDER INPUT TO MAKE CORRECTIONS AND THAT IS PRECISELY WHAT WAS NEEDED IN THIS INCIDENT TO REGAIN CTL. RPTR'S COMPANY IS ABOUT TO INSTALL HUD AND THIS WILL REQUIRE A HAND FLOWN ACFT ON APCH. HE FEELS THIS WILL BE A MUCH BETTER APCH. RPTR CALLED HIS CHIEF PLT AS HE IS A MEMBER OF THE SAFETY COMMITTEE AND WANTED TO PULL THE FLT DATA RECORDER. RPTR WAS IN THE PROCESS OF WRITING A SAFETY ARTICLE ON WAKE TURB AND GOT FIRST HAND KNOWLEDGE FOR THE ARTICLE.

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.