Narrative:

On the airway J-133 between hbk and anc going into anc, descending through FL180, captain set altimeter to 29.69 (correct altimeter was 28.69) and accidentally descended to 9750 ft. Copilot's altimeter was 28.69 (correct). Zan asked for our altitude, and we said we were climbing back to 10000 ft. The copilot warned me on descent about the low altimeter in anc. Upon descending through FL180, we set our altimeters and did our xchk and approach check. When I set my altimeter to 29.69 and his was 28.69, he should have caught it when I crosschecked my altitude with his. He did not mention anything when I crosschecked with 29.69 and 17800 ft. At that time his would have been 16800 ft and he didn't mention any discrepancy. I do not put the blame on any one person. I set the wrong altimeter and he failed to catch it in the xchk. Hopefully we will learn from our mistakes. The MEA was 9000 ft and the MOCA 8500 ft. Supplemental information from acn 425461: descending through 10000 ft MSL with a clearance to 10000 ft, copilot (PNF) crosschecked PF's altimeter, which displayed about 10600 ft MSL. I (PNF) made a verbal utterance while attempting to determine which altimeter was correct. PF realized I was indicating something seemed incorrect, and immediately disengaged autoplt and initiated climb to 10000 ft on my altimeter, bottoming at 9600 ft MSL. PF had set 29.69 instead of 28.69.

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Original NASA ASRS Text

Title: MD80 CREW DSNDED BELOW CLRED ALT.

Narrative: ON THE AIRWAY J-133 BTWN HBK AND ANC GOING INTO ANC, DSNDING THROUGH FL180, CAPT SET ALTIMETER TO 29.69 (CORRECT ALTIMETER WAS 28.69) AND ACCIDENTALLY DSNDED TO 9750 FT. COPLT'S ALTIMETER WAS 28.69 (CORRECT). ZAN ASKED FOR OUR ALT, AND WE SAID WE WERE CLBING BACK TO 10000 FT. THE COPLT WARNED ME ON DSCNT ABOUT THE LOW ALTIMETER IN ANC. UPON DSNDING THROUGH FL180, WE SET OUR ALTIMETERS AND DID OUR XCHK AND APCH CHK. WHEN I SET MY ALTIMETER TO 29.69 AND HIS WAS 28.69, HE SHOULD HAVE CAUGHT IT WHEN I XCHKED MY ALT WITH HIS. HE DID NOT MENTION ANYTHING WHEN I XCHKED WITH 29.69 AND 17800 FT. AT THAT TIME HIS WOULD HAVE BEEN 16800 FT AND HE DIDN'T MENTION ANY DISCREPANCY. I DO NOT PUT THE BLAME ON ANY ONE PERSON. I SET THE WRONG ALTIMETER AND HE FAILED TO CATCH IT IN THE XCHK. HOPEFULLY WE WILL LEARN FROM OUR MISTAKES. THE MEA WAS 9000 FT AND THE MOCA 8500 FT. SUPPLEMENTAL INFO FROM ACN 425461: DSNDING THROUGH 10000 FT MSL WITH A CLRNC TO 10000 FT, COPLT (PNF) XCHKED PF'S ALTIMETER, WHICH DISPLAYED ABOUT 10600 FT MSL. I (PNF) MADE A VERBAL UTTERANCE WHILE ATTEMPTING TO DETERMINE WHICH ALTIMETER WAS CORRECT. PF REALIZED I WAS INDICATING SOMETHING SEEMED INCORRECT, AND IMMEDIATELY DISENGAGED AUTOPLT AND INITIATED CLB TO 10000 FT ON MY ALTIMETER, BOTTOMING AT 9600 FT MSL. PF HAD SET 29.69 INSTEAD OF 28.69.

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.