JUST AT LIFTOFF AN ACR B737-300 EXPERIENCES 2 SHARP ROLLS WITH YAWING MOMENTS THAT ARE COUNTERED BY THE FLYING FO.

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JUST AFTER LIFTOFF RWY 22R EWR; AT APPROX 25 FT AGL AT APPROX V2 + 5 KTS WITH COPLT FLYING THE ACFT; AN UNEXPECTED ROLL AND YAW TO THE LEFT WAS ENCOUNTERED. COPLT MAINTAINED CTL WITH R AILERON AND RUDDER. COPLT ESTIMATED MAX BANK OF 5-10 DEGS AND LATER STATED HE THOUGHT IT MAY HAVE BEEN AN ENG FAILURE. HOWEVER; I (AS CAPT) CONFIRMED ENGS WERE OPERATING NORMALLY. INITIALLY I THOUGHT WE HAD ENCOUNTERED A WINDSHEAR. LAST RPTED WINDS BY TWR AT TKOF WERE 360 DEGS AT 4 KTS. NO TSTMS IN AREA. MAX THRUST WAS SET FOR TKOF DUE TO SLIGHT R QUARTERING TAILWIND. I MADE A PIREP OF POSSIBLE WINDSHEAR TO TWR. THERE WAS NO POSSIBILITY OF WAKE TURB BECAUSE A DASH 8 WAS THE PREVIOUS ACFT TAKING OFF BEFORE US (3 MINS) AND NO LARGE/HVY ACFT HAD LANDED PREVIOUSLY ON PARALLEL RWY AND DUE TO WIND DIRECTION; IT FELT TO ME AS THOUGH WE HAD TAKEN OFF IN WINDY CONDITIONS WITH YAW DAMPER OFF. TWR 10 MINS LATER STATED THE NEXT 2 ACFT TAKING OFF DID NOT ENCOUNTER ANY ABNORMAL CONDITIONS. FLT CONTINUED TO BOSTON THINKING IT WAS PROBABLY WIND. DURING CRUISE AFTER DISCUSSION WITH OTHER CREW MEMBERS; I FELT THERE MAY BE A MECHANICAL PROB WITH ACFT AND MADE A LOGBOOK ENTRY DESCRIBING SIT AFTER LNDG AT BOSTON. ACFT WAS TAKEN OUT OTS. FLT ATTENDANTS IN AFT JUMPSEAT DURING TKOF HEARD NOTHING ABNORMAL; BUT STATED THE BANK AT LOW ALT WAS SUCH THAT THEY FELT THE WINGTIP WAS GOING TO TOUCH THE GND. FLT ATTENDANTS STATED SEVERAL PAX REACTED AS THOUGH THEY NOTED SOMETHING HAD HAPPENED. ONE CUSTOMER APPARENTLY CALLED THE FAA WHOSE REPRESENTATIVE ARRIVED AT ACFT APPROX 10 MINS AFTER MY CREW DEPARTED FOR HOTEL FOR SCHEDULED OVERNIGHT STAY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS RPTR WAS THE PNF CAPT ON A B737-300 THAT EXPERIENCED A SUDDEN ROLL AND YAW JUST AFTER TKOF. HE SAID THAT FOR THE FIRST EVENT A L ROLL AND YAW; HE HAD NOT BEEN LOOKING OUTSIDE. HE HAD BEEN LOOKING AT THE INSTS TO ASSURE THAT THEY HAD A POSITIVE CLB RATE AFTER LIFTOFF WHEN HE FELT THE ABRUPT INPUT. THE FO ASKED IF THEY HAD HAD AN ENG FAILURE AND THE CAPT SAID NO AS THE ACFT THEN WAS ROLLING AND YAWING TO THE R. THIS SECOND MOVEMENT WAS MORE RAPIDLY COUNTERED BY THE FO. THESE EVENTS WERE RECORDED ON THE FLT DATA RECORDER AND LATER READ BY COMPANY MAINT DURING THE POST EVENT INVESTIGATION. AS PART OF THE INVESTIGATION ALL OF THE YAW DAMPER AND RUDDER PWR CTL UNIT COMPONENTS WERE BENCH TESTED BY THE COMPANY AND NO PROBS WERE FOUND. THE L ROLL BANK ANGLE WAS A MAX OF 7 DEGS AS SHOWN ON THE RECORDER. THE R ROLL WAS TO 10 DEGS. THE CAPT SAID THAT THESE FIGURES WERE CLOSE TO WHAT HE RECALLED. THE RECORDER ALSO INDICATED THAT THESE WERE RAPID ROLLS. AFTER THE BENCH TESTING WAS COMPLETE THE COMPONENTS WERE REINSTALLED ON THE ACFT AND NO PROBS HAVE BEEN RPTED.