Narrative:

At FL210 I copied tvc ATIS with altimeter setting 29.42. The first officer was flying. ATC (msp center 132.9) said they did not have our altitude reporting off of our transponder so I switched to #2 transponder. The first officer started his descent while I was off frequency calling company in range. When I was back on ATC frequency I noticed us going through FL180 and glanced at the first officer altimeter which was set at 30.42, so I set my altimeters to match his. We did our checklists. ATC said they still did not have our altitude reporting so I switched back to #1 transponder and recycled. We were vectored for the ILS 28 at tvc behind another aircraft to maintain 4000 ft then down to 2700 and cleared approach. We crossed the LOM at 2700 ft and noticed the GS was again working. So we followed it to a landing. Only after being parked at the gate and discussing possible causes for our GS problem did we notice the altimeters at 1600 ft not field elevation of 624 ft. We were very lucky the WX was such that we successfully made the approach. We crossed the LOM 1000 ft low! About 600 ft above terrain in the area. To prevent a recurrence of this deadly error I will always set the standby altimeter to ATIS or reported WX. Not 29.92 when in the flight levels. I will respond to checklist that altimeters are set and crosschecked with ATIS or WX and each other. I will include a radar altimeter is alive call and brief what a probable reading should be for a point prior to approach. This report might explain some of those controled flight into terrain accidents on approach.

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Original NASA ASRS Text

Title: ALTDEV ALT OVERSHOT IN DSCNT ALT READING DISCREPANCY. ALT XING RESTRICTION AT LOM NOT MET.

Narrative: AT FL210 I COPIED TVC ATIS WITH ALTIMETER SETTING 29.42. THE FO WAS FLYING. ATC (MSP CTR 132.9) SAID THEY DID NOT HAVE OUR ALT RPTING OFF OF OUR TRANSPONDER SO I SWITCHED TO #2 TRANSPONDER. THE FO STARTED HIS DSCNT WHILE I WAS OFF FREQ CALLING COMPANY IN RANGE. WHEN I WAS BACK ON ATC FREQ I NOTICED US GOING THROUGH FL180 AND GLANCED AT THE FO ALTIMETER WHICH WAS SET AT 30.42, SO I SET MY ALTIMETERS TO MATCH HIS. WE DID OUR CHKLISTS. ATC SAID THEY STILL DID NOT HAVE OUR ALT RPTING SO I SWITCHED BACK TO #1 TRANSPONDER AND RECYCLED. WE WERE VECTORED FOR THE ILS 28 AT TVC BEHIND ANOTHER ACFT TO MAINTAIN 4000 FT THEN DOWN TO 2700 AND CLRED APCH. WE CROSSED THE LOM AT 2700 FT AND NOTICED THE GS WAS AGAIN WORKING. SO WE FOLLOWED IT TO A LNDG. ONLY AFTER BEING PARKED AT THE GATE AND DISCUSSING POSSIBLE CAUSES FOR OUR GS PROBLEM DID WE NOTICE THE ALTIMETERS AT 1600 FT NOT FIELD ELEVATION OF 624 FT. WE WERE VERY LUCKY THE WX WAS SUCH THAT WE SUCCESSFULLY MADE THE APCH. WE CROSSED THE LOM 1000 FT LOW! ABOUT 600 FT ABOVE TERRAIN IN THE AREA. TO PREVENT A RECURRENCE OF THIS DEADLY ERROR I WILL ALWAYS SET THE STANDBY ALTIMETER TO ATIS OR RPTED WX. NOT 29.92 WHEN IN THE FLT LEVELS. I WILL RESPOND TO CHKLIST THAT ALTIMETERS ARE SET AND XCHKED WITH ATIS OR WX AND EACH OTHER. I WILL INCLUDE A RADAR ALTIMETER IS ALIVE CALL AND BRIEF WHAT A PROBABLE READING SHOULD BE FOR A POINT PRIOR TO APCH. THIS RPT MIGHT EXPLAIN SOME OF THOSE CTLED FLT INTO TERRAIN ACCIDENTS ON APCH.

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.