CAPT OF MLG ACR ACFT INADVERTENTLY DSNDED BELOW ASSIGNED ALT DUE TO DISTR.

Narrative

THE FLT WAS BEING CONDUCTED IN AN MLG ACFT FOR A SCHEDULED AIRLINE. WE WERE OPERATING A PAX CHARTER BTWN DENVER AND CODY; WY; FOR OUR COMMUTER AIRLINE. I AM A QUALIFIED CHK AIRMAN FOR BOTH THE MLG ACFT AND THE MORE ADVANCED AND AUTOMATED MLG Y. HOWEVER; I ONLY HAVE ABOUT 75 HRS IN THE MLG X AS COMPARED TO OVER 700 HRS IN THE MLG Y. THE FO IS ALSO A QUALIFIED CHK AIRMAN ON BOTH MODELS OF THE MLG WITH MANY THOUSANDS OF HRS IN THE MLG Y. I WAS SITTING IN THE L SEAT AND WAS FLYING THE ACFT AT THE TIME OF THE ALTDEV. WE WERE LEVEL AT FL350 WHEN WE RECEIVED A CLRNC TO DSND. WE ACCEPTED FL230 AND STARTED DOWN. DURING THE DSCNT THE OTHER PLT WAS ON THE #2 RADIO TALKING TO THE COMPANY AND WAS HAVING TROUBLE GETTING THE WX FOR CODY. WHILE HE WAS WAITING FOR THEM TO CALL BACK I WAS EXPLAINING TO HIM ABOUT THE AUTOMATED WX SVC AND HOW TO TUNE IT UP. SOMETIME DURING THE DSCNT WE HEARD 1 CHIME. SINCE HE IS VERY FAMILIAR WITH THE ACFT I ASKED HIM IF THAT WAS THE CABIN CREW TRYING TO CALL US. WE TRIED TO RAISE THEM ON THE INTERPHONE BUT TO NO AVAIL. JUST AFTER PASSING THROUGH 16000 FT I ASKED HIM WHAT ALT WE WERE CLRED TO. HE SAID THAT HE DIDN'T KNOW AS HE HAD BEEN ON AND OFF THE RADIO SINCE SHORTLY AFTER WE STARTED OUR DSCNT. WE BOTH AGREED THAT THE ALT INDICATOR WAS SET TO FL230. I LEVELED OFF AROUND 15500 FT AND IMMEDIATELY ASKED CTR WHAT ALT WE WERE CLRED TO AS WE HAD JUST PASSED 16000 FT. THE RESPONSE WAS 'AH; AH; I'M CHKING' OR SOMETHING SIMILAR TO THAT. FINALLY; THE CTLR CAME BACK ON AND SAID THAT HE HAD ONLY CLRED US DOWN TO FL230 BUT THAT WE WERE NOW CLRED TO 12000 FT. I CONTINUED THE DSCNT AND LEVELED OFF AT 12000 FT. I ASKED HIM POINT BLANK IF HE HAD A PROBLEM WITH THE ALTDEV AND HE SAID NO. DURING THE DSCNT FROM FL350 UNTIL WE REACHED 12000 FT WE WERE CLR OF CLOUDS AND HAD EXCELLENT INFLT VISIBILITY. THERE WERE ONLY 2 ACFT ON THE FREQ AND THE OTHER ACFT WAS NOT IN OUR AREA SECTOR. AFTER WE LEVELED AT 12000 FT WE HAD TO KEEP REQUESTING LOWER ALTS AS WE WERE IN AND OUT OF THE CLOUDS AND COULD NOT GET LOW ENOUGH TO SIGHT CODY VISUALLY. FINALLY; AT 10 MI SE OF THE ARPT WE BROKE THROUGH THE LAST CLOUD BANK AND MADE A VISUAL APCH INTO CODY. ONCE ON THE GND I CALLED THE SALT LAKE CTR AND SPOKE TO THE SUPVR. HE INDICATED THAT HE HAD NOT HEARD OF ANY ALT PROBLEMS BUT THAT HE WOULD CHK INTO IT. I TOLD HIM THAT I DID NOT WANT TO CAUSE ANY PROBLEMS AND THAT I WAS SATISFIED WITH HOW THE CTLR HAD HANDLED THE SITUATION. AGAINST MY WISHES; THE SUPVR INDICATED THAT HE WAS GOING TO TALK TO THE CTLR ON DUTY.