AN ACR MDT MISUNDERSTOOD ITS CLRNC AND STARTED AN APCH PREMATURELY. ALTDEV ALT EXCURSION.

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OUR FLT WAS OPERATING BTWN KALISPELL AND MISSOULA; MT. FROM AN ALT OF 16000 FT; CTR CLRED US DOWN TO 13000 FT. I WAS FLYING AS THE FO AND THE CAPT WAS OFF FREQ COPYING MISSOULA'S ATIS. WE WERE SWITCHED OVER TO MISSOULA'S APCH AND GIVEN THE CLRNC 'CLRED TO HUSON FIX VIA THE 13 DME ARC AND THE MSO 285 DEG RADIAL; MAINTAIN 13000 FT. EXPECT NO DELAYS; CLRED VOR/DME-A APCH.' AFTER GETTING ESTABLISHED ON THE ARC; WE LET DOWN IN ACCORDANCE WITH THE INST APCH PROC. WE BROKE OUT AA APPROX 9000 FT; CALLED THE FIELD IN SIGHT; AND REQUESTED A VISUAL APCH. THE APCH CTLR INFORMED US THAT WE HAD NOT BEEN CLRED OUT OF 13000 FT BUT NO TFC CONFLICT HAD OCCURRED AND WE COULD SWITCH TO TWR FOR THE VISUAL. I DON'T KNOW WHAT THE TAPE WOULD SHOW BUT THE CTLR SAID SHE CLRED TO HUSON FIX AND EXPECT THE APCH; MAINTAIN 13000 FT. THERE WAS TFC AHEAD WBOUND AT 12000 FT BUT CTR HAD NOT CALLED HER ABOUT ANY CONFLICTS AND OUR TCASII ON 10 NM RANGE HAD NO TARGETS ON IT LET ALONE A TA. I FEEL THE SIT COULD HAVE BEEN SOLVED IN EITHER OF 2 WAYS: 1) THE CTLR DID NOT ALERT US TO TFC AHEAD (WE FOUND OUT WHEN WE CALLED ON THE GND) THIS WOULD HAVE INCLUDED US IN THE TFC SIT AND WE WOULD HAVE BEEN MORE CONSCIOUS OF LEAVING 13000 FT. 2) PUT A HOLD ON THE MSO 340/13 AND DON'T CLR ACFT PAST IT UNLESS THE APCH AIRSPACE IS STERILE. SUPPLEMENTAL INFO FROM ACN 242550: AFTER LNDG; I VISITED THE TWR AND DISCUSSED THE INCIDENT WITH THE TWR MGR AND THE APCH CTLR. I WAS TOLD THAT OUR CLRNC WAS TO THE HUSON FIX; VIA THE 13 DME ARC; MAINTAIN 13000 FT; EXPECT NO DELAYS FOR THE VOR DME-A APCH. THIS IS THE CLRNC THAT MY FO RECEIVED WHILE I WAS OFF THE AIR. HE STATES THAT HE MISTOOK THIS FOR AN APCH CLRNC. THE FO ON THIS FLT WAS A FORMER MIL PLT WITH LITTLE OR NO PRIOR EXPERIENCE IN CIVIL AIRSPACE AND PROCS. THE CLRNC HE MISUNDERSTOOD WAS PROBABLY HIS FIRST EXPOSURE TO SUCH A CLRNC. (IN FACT; HE LATER STATED TO ME THAT HE HAD NEVER HEARD OF SUCH A CLRNC.) PERHAPS I ERRED IN NOT PERSONALLY VERIFYING THE APCH CLRNC WHEN I RETURNED TO THE ATC FREQ. HOWEVER; TO DO SO IS NOT COMPANY POLICY; NOR IS IT A PRACTICE AT OTHER CARRIERS (TO MY KNOWLEDGE). IT WILL; HOWEVER; BECOME PART OF MY TECHNIQUE IN THE FUTURE.