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

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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.