AN MD82 FLC EXPERIENCES A HEADING TRACK POS DEV DURING THE DEP PROC FROM SJC.

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WE DEPARTED SJC ARPT ON THE LOUPE 9 SID; RWY 30L. AT 1.8 DME THE FO (PF) REQUESTED 'HEADING SELECT 120 DEGS.' I SELECTED HDG 100 DEGS TO R. WITH OUR FLT DIRECTOR SYS YOU CANNOT GO FROM HDG 300 DEGS TO 120 DEGS BECAUSE THE SYS DOESN'T KNOW WHETHER TO MAKE THE 180 DEG TURN L OR R. .THEN AFTER THE TURN IS COMMENCED; WE TWEAK THE HEADING SELECT KNOB TO 120 DEGS. WITH THE CONCERN FOR THE RPTED AND PREVAILING ICING CONDITIONS; I FAILED TO TWEAK IT TO 120 DEGS. I TURNED ON THE ENG ANTI-ICE OUT OF 3500 FT MSL. AT OUR ASSIGNED ALT OF 5000 FT; THE FO (PF) TURNED ON THE AUTOPLT. AT THIS POINT THE PF TAKES OVER OPERATING AUTOPLT AND FLT DIRECTOR KNOBS. WE WERE NOW CLRED AT 6.3 DME TO 'TURN R PLT DISCRETION; CROSS SJC VOR AT 12000 FT AND RESUME THE LOUPE DEP; MAINTAIN FL230.' THE FO (PF) STARTED THE AUTOPLT CLB. OUT OF 8000 FT THE DEP CTLR ASKED OUR HEADING. I RESPONDED 'COMING R HDG 120 DEGS.' HE SAID 'TURN R HDG 180 DEGS.' I RESPONDED AND WE TURNED. WE HAD A STRONG W WIND. OUT OF 11000 FT HE HAD US 'TURN R 300 DEGS DIRECT THE VOR; RESUME THE LOUPE.' HE WAS VECTORING US AT THIS POINT BEHIND A DEPARTING DC8 HVY; WHO WAS RPTING MODERATE ICING. WE HAD ONLY A TRACE OF ICE. THE FLT WAS COMPLETED WITHOUT INCIDENT. WITH THE TURB; ICING CONDITIONS; AND DEP WORKLOAD; WE FAILED TO SET THE CORRECT HEADING.