Narrative:

On descent into slc, ZLC cleared flight to fly the spane 3 arrival, cross spane at 16000 ft. While crossing spane at 16000 ft, captain was on company radio and not monitoring ATC. After spane, first officer began a descent to 11000 ft (expected crossing at boagy intersection). Since captain was off the radio, he did not hear any ATC transmission prior to the descent. Upon return from calling company, I (captain) asked first officer if we were cleared to 11000 ft and he replied that we were. At about 14000 ft, ATC queried our altitude and indicated that our clearance altitude was 16000 ft. We were instructed to maintain 12000 ft, then cleared to 10000 ft. No TCASII advisories or traffic conflicts arose. Flight continued and landed normally. Captain did not monitor ATC during call to company, and was unable to know that no further descent clearance below 16000 ft had been given. First officer did not properly comply with descent clearance. Supplemental information from acn 499390: inbound on flight abcd from denver to salt lake city, at approximately XA50Z, we had a misunderstanding of our clearance. As first officer, I was the PF. In cruise at FL310, I understood our clearance to be 'cleared to the slc airport and descend via the spane 3 arrival.' once level at 16000 ft, just before spane intersection, I dialed in 11000 ft in the altitude alert window, and just past spane I began a descent in order to cross boagy intersection at 11000 ft. Captain was on the interphone (as I recall) and came back onto center frequency as we crossed spane intersection. Moments later, center questioned us as to whether we had been cleared 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 clearance. And, perhaps having dialed in 11000 ft in the altitude alert window just crossing spane intersection, I inferred that the captain also understood us to be cleared to descend via the spane 3 arrival, as he did not challenge the altitude I had selected in the altitude alert window. In the future, I will utilize aggressive CRM techniques to make absolutely certain I have heard the clearance correctly, understand it properly, and that the captain agrees with it.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.