FLC OF AN MLG ACR ACFT DSNDED BELOW ASSIGNED AND PUBLISHED FINAL APCH MINIMUMS DUE TO DISTR OF AN ACFT EQUIP PROB AND SETTING UP FOR AN APCH CHANGE ASSIGNMENT.

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I WAS FLYING THE AIRPLANE. WE WERE APCHING MKE FROM THE SSE. THE APCH CTLR TOLD US TO EXPECT ILS RWY 19R. WE SET UP FOR THE APCH (FMS; FREQS TUNED AND IDENTED; ETC). WE WERE IN A DSCNT TO 2500 FT AT THE TIME; AND HAD BEEN IN A LONG CONTINUOUS DSCNT. THE CTLR REASSIGNED US LOC 25L APCH DUE TO SOME WX W AND N OF MKE THAT WAS MOVING TOWARD THE FINAL APCH COURSE OF RWY 19R. WE AGREED. WE WERE AT 180 KTS; THE GEAR WAS LOWERED TO EXPEDITE OUR DSCNT. FROM OUR POS INTERCEPTING LOC 25L WAS CONSIDERABLY CLOSER THAN RWY 19R LOC WOULD HAVE BEEN. THE FO HURRIEDLY SET US UP FOR RWY 25L APCH. I LOCATED THE 25L LOC APCH PAGE AND SET MY EFIS PANEL UP FOR THE APCH. DURING THIS TIME WE GOT A HYD PRESSURE MESSAGE ON THE MFDU ACCOMPANIED BY A #1 TRIM FAULT MESSAGE ON THE OTHER MFDU. WE CHKED THE HYD PANEL AND GAUGES. THEY APPEARED NORMAL. THE TRIM FAULT WAS RESET. SHORTLY AFTER THIS THE APCH CTLR SAID HE HAD A LOW ALT ALERT ON US. WE IMMEDIATELY CHKED OUR ALT. WE WERE AT 1500 FT. WE INITIATED AN IMMEDIATE CLB AND LEVELED AT 2500 FT. 2500 FT WAS STILL SHOWING IN THE ALT SET WINDOW. THE AUTOPLT WAS STILL ON. THE AUTO THROTTLES FOR SOME REASON HAD DROPPED OFF; HOWEVER. THEY WERE RESET AND FUNCTIONED NORMALLY THE REST OF THE FLT; AS DID THE TRIM FAULT. WE DID NOT GET AN ALTDEV AURAL WARNING BECAUSE THIS ALERT IS INHIBITED WITH THE LNDG GEAR DOWN. I DO NOT KNOW WHY THE AUTOPLT DID NOT CAPTURE THE ALT.