ALT OVERSHOT DURING AN ATTEMPTED VMC APCH BY A B767 FLC WHEN THE CREW FORGETS TO RESET THEIR ALTIMETERS FROM QNE TO LCL QNH GOING THROUGH THE 5500 FT TRANSITION LEVEL FOR ILS RWY 25 AT EBBR; FO.

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ON APCH TO RWY 25L AT BRU WITH MULTIPLE ERRONEOUS INDICATIONS DUE TO AN AIR GND SENSOR FAILURE. I WAS AVOIDING ICING BY EXPEDITING THROUGH AN OPENING IN A BROKEN LAYER BTWN 6000 FT AND 4000 FT. OVER BRU; OUR CLRNC WAS FROM FL80 TO 2000 FT. TRANSITION LEVEL WAS 5500 FT. I WAS FOCUSED ON GETTING THE ACFT THROUGH THE BROKEN LAYER AND FAILED TO RESET MY ALTIMETERS. ATC POINTED OUT TFC TO US AS WE PASSED 4500 FT. WE DID NOT SEE IT VISUALLY; BUT HAD IT ON TCASII. IT WAS AT 2000 FT AT OUR 9 O'CLOCK POS AND PASSED WELL BEHIND US. BOTH PLTS WERE LOOKING FOR THE TFC AS WE PASSED THROUGH 4000 FT. AT 3500 FT; I COULD SEE THE FIELD AND WE WERE ALWAYS IN VFR CONDITIONS. ATC CLRED US TO INTERCEPT THE LOC FOR RWY 25L. ATC INSTRUCTED US TO MAINTAIN 2000 FT UNTIL ESTABLISHED ON THE ILS TO RWY 25L. THIS CALL COINCIDED WITH THE RADIO ALTIMETER CALL AT 2500 FT. WE INTERCEPTED THE ILS AT ABOUT 2300 FT. I WAS LEVELING AT 2000 FT WHEN ATC INSTRUCTED US TO CLB TO 2000 FT AND RESET OUR ALTIMETERS. I CLBED TO 2000 FT AND RESET ALTIMETERS. OUR FAILURE TO SET THE APPROPRIATE ALTIMETER SETTING LED US TO ABOUT 500 FT LOW. WE USED PROPER PROC TO SET AND VERIFY MCP ALTS. I BELIEVE WORKLOAD INDUCED BY MULTIPLE ERRONEOUS INDICATIONS IN THE COCKPIT DUE TO AIR GND SENSOR FAILURE; AVOIDING ICING; AND THE TFC CALLS FROM ATC; ALL CONTRIBUTED TO OUR FAILURE TO SET THE ALTIMETERS. WE WERE IN VFR AT ALL TIMES.