B737-200 CREW HAD ALTDEV IN ZLC CLASS E AIRSPACE.

Narrative

ON DSCNT INTO SLC; ZLC CLRED FLT TO FLY THE SPANE 3 ARR; CROSS SPANE AT 16000 FT. WHILE XING SPANE AT 16000 FT; CAPT WAS ON COMPANY RADIO AND NOT MONITORING ATC. AFTER SPANE; FO BEGAN A DSCNT TO 11000 FT (EXPECTED XING AT BOAGY INTXN). SINCE CAPT WAS OFF THE RADIO; HE DID NOT HEAR ANY ATC XMISSION PRIOR TO THE DSCNT. UPON RETURN FROM CALLING COMPANY; I (CAPT) ASKED FO IF WE WERE CLRED TO 11000 FT AND HE REPLIED THAT WE WERE. AT ABOUT 14000 FT; ATC QUERIED OUR ALT AND INDICATED THAT OUR CLRNC ALT WAS 16000 FT. WE WERE INSTRUCTED TO MAINTAIN 12000 FT; THEN CLRED TO 10000 FT. NO TCASII ADVISORIES OR TFC CONFLICTS AROSE. FLT CONTINUED AND LANDED NORMALLY. CAPT DID NOT MONITOR ATC DURING CALL TO COMPANY; AND WAS UNABLE TO KNOW THAT NO FURTHER DSCNT CLRNC BELOW 16000 FT HAD BEEN GIVEN. FO DID NOT PROPERLY COMPLY WITH DSCNT CLRNC. SUPPLEMENTAL INFO FROM ACN 499390: INBOUND ON FLT ABCD FROM DENVER TO SALT LAKE CITY; AT APPROX XA50Z; WE HAD A MISUNDERSTANDING OF OUR CLRNC. AS FO; I WAS THE PF. IN CRUISE AT FL310; I UNDERSTOOD OUR CLRNC TO BE 'CLRED TO THE SLC ARPT AND DSND VIA THE SPANE 3 ARR.' ONCE LEVEL AT 16000 FT; JUST BEFORE SPANE INTXN; I DIALED IN 11000 FT IN THE ALT ALERT WINDOW; AND JUST PAST SPANE I BEGAN A DSCNT IN ORDER TO CROSS BOAGY INTXN AT 11000 FT. CAPT WAS ON THE INTERPHONE (AS I RECALL) AND CAME BACK ONTO CTR FREQ AS WE CROSSED SPANE INTXN. MOMENTS LATER; CTR QUESTIONED US AS TO WHETHER WE HAD BEEN CLRED BELOW 16000 FT. WE QUICKLY REALIZED WE HAD A MISUNDERSTANDING AND PROMPTLY CORRECTED TO 12000 FT AND THEN TO 10000 FT AS PER ATC REQUEST. APPARENTLY; I 'MISHEARD' THE CLRNC. AND; PERHAPS HAVING DIALED IN 11000 FT IN THE ALT ALERT WINDOW JUST XING SPANE INTXN; I INFERRED THAT THE CAPT ALSO UNDERSTOOD US TO BE CLRED TO DSND VIA THE SPANE 3 ARR; AS HE DID NOT CHALLENGE THE ALT I HAD SELECTED IN THE ALT ALERT WINDOW. IN THE FUTURE; I WILL UTILIZE AGGRESSIVE CRM TECHNIQUES TO MAKE ABSOLUTELY CERTAIN I HAVE HEARD THE CLRNC CORRECTLY; UNDERSTAND IT PROPERLY; AND THAT THE CAPT AGREES WITH IT.