ACFT EQUIP PROB UNCOMMANDED R ROLL THAT MAY HAVE BEEN CAUSED BY AIRFRAME ICING. ALT DEVIATION DUE TO MISSET ALTIMETER.

Narrative

JUST AFTER INITIATING A DSCNT FROM FL200 TO 10000 FT; WE ENCOUNTERED A FLT CTL MALFUNCTION. THE PROB WAS INITIALLY MASKED BY THE AUTOPLT UNTIL ITS CTL CAPABILITY WAS EXCEEDED. THE AUTOPLT WAS DISCONNECTED AND THE AIRPLANE ABRUPTLY ROLLED TO THE R. AFTER THE INITIAL RECOVERY; WE ENCOUNTERED CONTINUED DIFFICULTY IN ACHIEVING STABILIZED FLT. THIS STRUGGLE WITH ACFT CTL LASTED FOR APPROX 5000- 6000 FT IN THE DSCNT. WE DSNDED THROUGH TRANSITION LEVEL WITHOUT RESETTING THE ALTIMETER TO THE PROPER READING. UPON LEVELING OFF AT 10000 FT WE WERE ADVISED BY SEA APCH OF THE CURRENT ALTIMETER SETTING. WHEN THE NEW SETTING WAS PUT IN; IT THEN BECAME APPARENT THAT WE WERE JUST UNDER 300 FT OFF ALT AND THE PROPER ALT WAS IMMEDIATELY REACQUIRED. BOTH PLTS WERE INVOLVED IN REACQUIRING CTL OF THE ACFT DURING THE FLT CTL MALFUNCTION. THESE ACTIONS WERE TAKING PLACE DURING THE PERIOD OF PASSING THROUGH THE TRANSITION LEVEL WHEN THE LCL ALTIMETER IS NORMALLY DIALED IN. AFTER STABILIZED FLT WAS ACHIEVED; WE WERE AT AN ALT WHERE THE NORMAL COCKPIT CUES TO RESET THE ALTIMETER (IE; PASSING FL180) WERE NOT PRESENT. CONSEQUENTLY THIS ACTION; DONE IN ASSOCIATION WITH THE APCH CHK; DID NOT OCCUR. THE FLT CTL MALFUNCTION AND ASSOCIATED RECOVERY ACTIONS PROVIDED SUFFICIENT DISTR SO THAT BOTH PLTS OVERLOOKED THE APCH CHKLIST. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES THE MD80. THERE HAD BEEN RAIN AT PDX PRIOR TO DEP. THE RPTR THINKS THAT ONE OR MORE OF THE SPOILERS MAY HAVE BEEN FROZEN DOWN TO CAUSE THE ROLL. THE FLT WAS IN IMC FOR MOST OF THE TIME. THE CREW DISCUSSED THE ROLL AFTER THE AUTOPLT TRIPPED OFF AND DECIDED ON THE POSSIBILITY OF CTL ICING. THEY TRIED THE SPOILERS AGAIN WITH THE SAME RESULTS -- 40 DEGS R ROLL WITH ABOUT 20 DEGS NOSE DOWN. THE SPOILERS SEEMED TO WORK PROPERLY WHEN ON THE GND. THE RPTR WROTE THIS IN THE LOGBOOK AND WENT TO ANOTHER ACFT AS SCHEDULED. HE HAS NOT HEARD FROM THE MAINT DEPT WHAT THE CORRECTIVE ACTION MAY HAVE BEEN. THE ALT DISCREPANCY WAS CAUSED BY AN UNUSUALLY LOW ALTIMETER SETTING AND THE DISTR OF THE CTL PROB. ARTCC DID NOT ANNOUNCE THE LOW SETTING AND DID NOT SEEM CONCERNED WITH THE LOW LEVELOFF. HE HAS NOT HEARD FROM THE FAA ON THE ALT NOR THE CTL PROB.