UNCOMMANDED ROLL ON FINAL APCH -- HAPPENED TWICE AT SAME ARPT.

Narrative

DAY VFR; RIVER RWY 18; B757 7 MI AHEAD; WIND 220 DEGS/18 KTS/GUSTING 26. HAND FLOWN APCH AT APPROX 150 FT AGL THE AIRPLANE STARTED TO ROLL L AND R APPROX 15 DEGS AOB 4-5 TIMES. EXECUTED MISSED APCH. AT LEVEL OFF WE DISCUSSED CAUSES AND OPTIONS. ELECTED TO ATTEMPT ANOTHER RIVER VISUAL RWY 18. SYSTEMS OK TILL THE FLARE; ROLL STARTED AGAIN. LANDED ACFT AUTOTHRUST DISENABLED. WE GNDED ACFT AND HAD LENGTHY CONFERENCE CALL WITH THE COMPANY MAINT FOUND NOTHING WRONG WITH AIRPLANE. CREW ELECTED TO GO DCA-DTW. THAT LEG WENT WITHOUT INCIDENT (VISUAL RWY 21R DTW GUSTY R XWIND). TOOK SAME ACFT TO BWI (DTW-BWI). LEVEL FLT AUTOPLT ENGAGED AT FL280 280 KTS NOTED SMALL BUT RAPID ROLLS AND HAD A FLT COMPUTER FAILURE (ELEVATOR AILERON COMPUTER 1). WE ELECTED TO RESET COMPUTER. SAME SIT OCCURRED. TURNED ELEVATOR AILERON COMPUTER 1 OFF AND LANDED BUT WITHOUT INCIDENT. WE ARE NOT SURE IF IT WAS ENVIRONMENTAL (TWR RPTED 10 KTS LOSS OF AIRSPD ON FINAL) (NO AIRSPD LOSS WAS NOTED) OR A SYS PROB. IT IS STILL UNDER INVESTIGATION. I WOULD NOT HAVE CHANGED MY DECISIONS BECAUSE WE RECOGNIZED THE PROB AND TOO IMMEDIATE ACTION (MISSED APCH) THEN GOT AS MANY PEOPLE INVOLVED IN THE DECISION PROCESS AS WE COULD. (ON 2ND LNDG A 727 TOOK OFF AHEAD OF US). OUR TRAINING AND ABILITY TO TALK OPENLY ABOUT THE SIT I FEEL LED TO TIMELY SAFE CONCLUSIONS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: THOUGH; UNABLE TO CONTACT THE RPTR; ANOTHER PLT WITH THE SAME COMPANY; HAD PREVIOUSLY SENT A RPT AND ON THAT CALLBACK MENTIONED THIS INCIDENT. HE HAD BEEN THE A320 AIR SAFETY REPRESENTATIVE WHEN THE COMPANY DEBRIEFED THE INCIDENT. HE HAD ALSO SAID IF HE COULD BE OF FURTHER ASSISTANCE HE WOULD BE HAPPY TO HELP; SO A CALL WAS MADE TO THAT PLT. HE SAID THAT THEIR COMPANY HAD PREVIOUSLY REQUIRED APCHS WITH THE A320 TO BE MADE WITH FLAPS 3 DEGS AT DCA FOR NOISE ABATEMENT; BUT AFTER THIS INCIDENT THAT WAS DISCONTINUED AND FULL FLAPS ARE NOW USED. HE ALSO SAID THAT WITH FLAPS 3 DEGS; THE CTLS ARE MORE SENSITIVE. THE COMPANY FINAL RESOLUTION OF THIS INCIDENT WAS THAT THE ROLLS ON FINAL APCH WERE PLT INDUCED. IT WOULD APPEAR TO THIS ANALYST THAT THE USE OF FLAPS 3 DEGS WAS A POOR PROC FOR SEVERAL REASONS: 1) CAUSES THE FLT CTLS TO BE MORE SENSITIVE IN A MORE DIFFICULT THAN USUAL APCH; 2) THE A320 IS ONE OF A FEW ACFT THAT IS UNRESTR AT NATIONAL BECAUSE OF IT'S LOW NOISE PROFILE AND 3) THE RWY IS SHORTER THAN MOST AND FLAPS 3 DEGS REQUIRES EXTRA GND ROLL DUE TO EXTRA SPD. SUPPLEMENTAL INFO FROM ACN 303407: UNABLE TO CTL AIRPLANE; DID A GAR. ON SECOND LNDG IT HAPPENED AGAIN JUST PRIOR TO LNDG. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: THE RPTR FLIES THE A-320 FOR A MAJOR UNITED STATES ACR. THIS INCIDENT WAS WRITTEN UP IN THE ACFT LOGBOOK AND 'GND CHKED OK' BY DCA MAINT. LATER THAT DAY; THE SAME CREW HAD SOME UNWANTED AILERON INPUT IN CRUISE. ANOTHER CREW HAD ANOTHER INCIDENT WHERE THERE WAS ANOTHER UNWANTED AILERON INPUT. THE ACFT WAS THEN TAKEN OTS AND MAINT FOUND THAT THERE WERE SPURIOUS INPUTS FROM THE FO'S CTL STICK. THE RPTR BELIEVES 'THAT THE ACFT DID SOMETHING ON ITS OWN' AND THAT THERE WAS NO WAKE TURB.