PLTS WERE HAVING TROUBLE OPERATING A NEWLY INSTALLED GPS COM SYS.

Narrative

AFTER LEAVING THE AIRWAY ON AN INITIAL VECTOR TO INTERCEPT THE FINAL APCH COURSE TO RWY 31L ILS AT BFI; PF ATTEMPTED TO LOAD APCH INTO II MORROW GX 60 GPS/COM. BOX STATED: NO APCHS AVAILABLE; BFI 345 NM. SINCE THIS WAS OBVIOUSLY FALSE; BOTH PLTS SPENT THE NEXT 10 MINS OR SO TRYING TO PROGRAM THE BOX; WHILE HEARING SEA APCH TALKING TO NUMEROUS OTHER ACFT. AFTER A WHILE; BOTH PLTS BEGAN TO WONDER WHAT APCH HAD IN MIND; SINCE WE WERE HEADED FOR A MOUNTAIN. AT THE INSTANT WE DECIDED TO QUERY APCH; WE BOTH LOOKED AT THE GPS COM AND SAW BOTH ACTIVE AND STANDBY FREQS WERE ONES THAT HAD NEVER BEEN ASSIGNED TO US; ALTHOUGH THE ACTIVE FREQ WAS A SEA APCH FREQ; HENCE THE CONSTANT CHATTER. WE LOOKED AT THE PAPER LOG; PICKED UP THE CORRECT FREQ; CALLED WITH AN APOLOGY FOR BEING NORDO FOR X MINUTES; AND WERE SOMEWHAT PEEVISHLY GIVEN A 90 DEG L TURN TO INTERCEPT. NOT SURPRISING UNDER THE CIRCUMSTANCES! THE REST OF THE APCH PROCEEDED NORMALLY. ON THE GND; BOTH PLTS WERE AT A LOSS TO EXPLAIN HOW THE EXTRANEOUS FREQS GOT LOADED INTO THE BOX. PLT/OWNER HAS HAD THE APCH-CERTIFIED GX-60 FOR ABOUT 6 MONTHS AND SAID HE SPENT MANY HRS WITH THE PC TRAINING SOFTWARE AND FELT QUITE COMFORTABLE WITH IT. INSTRUCTOR (ME) HAS HAD A II MORROW APOLLO 2001 FOR 7 YRS; SO IS VERY FAMILIAR WITH OPERATING LOGIC OF THE UNIT; IF NOT WITH THE APCH MODES. SOMEHOW; THIS BOX LOADED AN ACTIVE SEA APCH FREQ WITHOUT OUR KNOWING IT; AND SINCE THE CHATTER WAS ESSENTIALLY IDENTICAL WITH WHAT WE EXPECTED TO HEAR; WE WERE UNAWARE UNTIL THE END THAT IT WASN'T THE FREQ WE HAD BEEN ASSIGNED LAST. SINCE WE WERE SO FAR S (30 MI) OF THE ARPT; WE NEVER ACTUALLY FLEW THROUGH THE LOC; WHICH WOULD HAVE ALERTED US. EVEN THOUGH IT WAS CAVU AND WE NEVER GOT VERY CLOSE TO THE RISING TERRAIN; IT WAS WHAT GOT OUR ATTN! IN IMC; WHO KNOWS WHETHER WE WOULD HAVE FIGURED IT OUT IN TIME. AFTER THIS EXPERIENCE; I WILL NEVER BUY A COMBINED GPS/COM BOX; AND IF IT EVENTUALLY BECOMES NECESSARY; I'LL STILL HAVE A DEDICATED PRIMARY COM RADIO! SINCE WE WERE NEVER ASKED TO CALL THE FACILITY; WE ASSUMED THAT THERE WERE NO SEPARATION BUSTS. WE ALSO NEVER FOUND OUT HOW LONG WE WERE NORDO; IT COULD HAVE BEEN ANYTHING FROM 3-10 MINS. IN CLOSING; I MIGHT POINT OUT THAT 2 EXPERIENCED AND CURRENT INST RATED AND COMMERCIAL PLTS WERE LED DOWN THE PRIMROSE PATH BY THIS BOX FOR LONG ENOUGH TO HAVE FLOWN INTO TERRAIN. WHAT CHANCE DOES THE AVERAGE PVT PLT WITH A FRESH INST TICKET HAVE?