Narrative:

Slc center cleared my flight to what I thought was 11000' MSL and to cross the ffu VOR at that altitude. I read back that clearance to slc center while my first officer was busy on another radio getting ATIS for landing. I read back: 'I believe you said 11000' at the fairfield VOR.' there was no response from ATC. While descending through 13800' MSL, ATC asked what our altitude was and informed us that our cleared altitude was 17000' MSL! ATC then cleared us to maintain 13000' MSL. Flight continued uneventfully to landing. Several factors probably contributed to this event: my misunderstanding of the original clearance to 17000', my indirect questioning of ATC concerning the cleared altitude, ATC failed to correct my readback, this was not a 2-M cockpit crew in this situation since I was both flying and talking to ATC--first officer was not in loop because of other cockpit duties not in loop, my neglecting to verify MCA in mountainous terrain by reference to area chart--numerous mtn peaks above 10000' MSL in area!! Supplemental information from acn 82314: after landing we contacted the sector supervisor on the phone to inquire about terrain clearance as nobody had noticed a 3200' deviation. He informed us the computer will only alert the controller if there is a traffic conflict (there was nobody out there but us) or if we had continued down below the minimum terrain clearance altitude for the area 10000-11000'. The controller just happened to notice our mode C.

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Original NASA ASRS Text

Title: ACR MLG READ BACK WRONG ALT AND WAS IN CTLED FLT TOWARD TERRAIN.

Narrative: SLC CENTER CLRED MY FLT TO WHAT I THOUGHT WAS 11000' MSL AND TO CROSS THE FFU VOR AT THAT ALT. I READ BACK THAT CLRNC TO SLC CENTER WHILE MY F/O WAS BUSY ON ANOTHER RADIO GETTING ATIS FOR LNDG. I READ BACK: 'I BELIEVE YOU SAID 11000' AT THE FAIRFIELD VOR.' THERE WAS NO RESPONSE FROM ATC. WHILE DSNDING THROUGH 13800' MSL, ATC ASKED WHAT OUR ALT WAS AND INFORMED US THAT OUR CLRED ALT WAS 17000' MSL! ATC THEN CLRED US TO MAINTAIN 13000' MSL. FLT CONTINUED UNEVENTFULLY TO LNDG. SEVERAL FACTORS PROBABLY CONTRIBUTED TO THIS EVENT: MY MISUNDERSTANDING OF THE ORIGINAL CLRNC TO 17000', MY INDIRECT QUESTIONING OF ATC CONCERNING THE CLRED ALT, ATC FAILED TO CORRECT MY READBACK, THIS WAS NOT A 2-M COCKPIT CREW IN THIS SITUATION SINCE I WAS BOTH FLYING AND TALKING TO ATC--F/O WAS NOT IN LOOP BECAUSE OF OTHER COCKPIT DUTIES NOT IN LOOP, MY NEGLECTING TO VERIFY MCA IN MOUNTAINOUS TERRAIN BY REF TO AREA CHART--NUMEROUS MTN PEAKS ABOVE 10000' MSL IN AREA!! SUPPLEMENTAL INFO FROM ACN 82314: AFTER LNDG WE CONTACTED THE SECTOR SUPVR ON THE PHONE TO INQUIRE ABOUT TERRAIN CLRNC AS NOBODY HAD NOTICED A 3200' DEVIATION. HE INFORMED US THE COMPUTER WILL ONLY ALERT THE CTLR IF THERE IS A TFC CONFLICT (THERE WAS NOBODY OUT THERE BUT US) OR IF WE HAD CONTINUED DOWN BELOW THE MINIMUM TERRAIN CLRNC ALT FOR THE AREA 10000-11000'. THE CTLR JUST HAPPENED TO NOTICE OUR MODE C.

Data retrieved from NASA's ASRS site as of August 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.