MD80 FLC RESOLVE COMPASS EQUIP PROB WITH I80 APCH CTL.

Narrative

AS SOON AS WE STARTED TO TURN AFTER TKOF; WE REALIZED THAT THERE WAS A 30 DEG ERROR BTWN OUR 2 COMPASS SYS; BUT WE DIDN'T KNOW WHICH ONE WAS CORRECT. DEP TOLD US TO GO DIRECT IDU VOR; BUT THE RMI NEEDLES WERE POINTING 30 DEGS APART ALSO. I PICKED ONE (TURNED OUT TO BE THE WRONG ONE) AND FO TOLD CTLR THAT WE HAD AN INST 'ANOMALY' AND ASKED IF IT LOOKED LIKE WE WERE HEADED TO IDU. CTLR SAID WE NEEDED ABOUT 10 DEGS R; WHICH DIDN'T HELP BECAUSE THAT WAS 1/2 WAY BTWN THE RMI NEEDLES. A SHORT TIME LATER; DEP ASKED OUR HDG. I TOLD HIM OUR HDG AND EXPLAINED IN A LITTLE MORE DETAIL THAT WE HAD A COMPASS PROB. HE CAME BACK WITH 'MAKE AN IMMEDIATE R TURN;' WHICH OF COURSE MEANS THAT THERE IS A CONFLICT OF SOME KIND. WE FINALLY GOT STABILIZED ON A COURSE TO THE VOR (SO WE NOW KNOW WHICH SYS WAS CORRECT). I MANUALLY SLAVED THE BAD SYS TO THE GOOD ONE AND IT STAYED THAT WAY FOR THE REST OF THE FLT. IN HINDSIGHT; YOU COULD SAY WE SHOULD HAVE NOTICED THE DIFFERENCE BEFORE THE TKOF ROLL (IF IT WAS PRESENT THEM). BUT IT IS NOT A COMMON PROB AND WHEN IT DOES OCCUR THE COMPARATOR ALWAYS GIVES A WARNING. PROBABLY THE BEST THING WE COULD HAVE DONE WAS BE MORE SPECIFIC ABOUT THE PROB WITH THE CTLRS IMMEDIATELY.