Narrative:

We were level at 17000 ft MSL, 250 KTS on landr 2 arrival to den. Approach cleared us to 7000 ft MSL. First officer confirmed '7000 ft' and set it in MCP altitude. I (PNF) confirmed readback and setting. While descending through approximately 12400 ft, approach asked to what altitude we were descending. First officer stated '7000 ft.' he instructed to level at 11000 ft, that we had been cleared to 13000 ft. We did so, continuing to a normal approach and landing. There was no traffic conflict. Subsequent discussion: 1) between pilots -- both recall 7000 ft and confirming it on readback. 2) between ATC and me -- I was told again (by telephone) cleared to 13000 ft, said he confirmed it on the tape. Speculation (ATC): at time of altitude change, ATC told us to 'expect' runway 7. He believes we confused it with 7000 ft altitude. Speculation (pilots): at the time, we were in and out of clouds and moderate turbulence. But, we were both convinced we had heard correctly. If our error, neither of us had ever done such a thing before. Between us, we questioned whether we had actually received descent to 7000 ft, that it was an ATC error. Recommendation: the only recommendation, though perhaps not practical, is to segregate altitude instructions from all other ATC communications.

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Original NASA ASRS Text

Title: B757 ALTDEV ARRIVING DEN.

Narrative: WE WERE LEVEL AT 17000 FT MSL, 250 KTS ON LANDR 2 ARR TO DEN. APCH CLRED US TO 7000 FT MSL. FO CONFIRMED '7000 FT' AND SET IT IN MCP ALT. I (PNF) CONFIRMED READBACK AND SETTING. WHILE DSNDING THROUGH APPROX 12400 FT, APCH ASKED TO WHAT ALT WE WERE DSNDING. FO STATED '7000 FT.' HE INSTRUCTED TO LEVEL AT 11000 FT, THAT WE HAD BEEN CLRED TO 13000 FT. WE DID SO, CONTINUING TO A NORMAL APCH AND LNDG. THERE WAS NO TFC CONFLICT. SUBSEQUENT DISCUSSION: 1) BTWN PLTS -- BOTH RECALL 7000 FT AND CONFIRMING IT ON READBACK. 2) BTWN ATC AND ME -- I WAS TOLD AGAIN (BY TELEPHONE) CLRED TO 13000 FT, SAID HE CONFIRMED IT ON THE TAPE. SPECULATION (ATC): AT TIME OF ALT CHANGE, ATC TOLD US TO 'EXPECT' RWY 7. HE BELIEVES WE CONFUSED IT WITH 7000 FT ALT. SPECULATION (PLTS): AT THE TIME, WE WERE IN AND OUT OF CLOUDS AND MODERATE TURB. BUT, WE WERE BOTH CONVINCED WE HAD HEARD CORRECTLY. IF OUR ERROR, NEITHER OF US HAD EVER DONE SUCH A THING BEFORE. BTWN US, WE QUESTIONED WHETHER WE HAD ACTUALLY RECEIVED DSCNT TO 7000 FT, THAT IT WAS AN ATC ERROR. RECOMMENDATION: THE ONLY RECOMMENDATION, THOUGH PERHAPS NOT PRACTICAL, IS TO SEGREGATE ALT INSTRUCTIONS FROM ALL OTHER ATC COMS.

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.