As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW WAS DESCENDING TO KMDW WHEN ADC #2 ALTITUDE TAPE FAILED ON FO SCREEN. CREW DECLARED AN EMERGENCY AS THEY WERE APPROACHING CLASS B AIRSPACE. CREW RAN CHECKLIST AND PERFORMED A REVERSION TO THE #1 ADC. LANDED WITHOUT INCIDENT. MAINTENANCE WENT TO AIRCRAFT POWERED UP ALL SYSTEMS AND COULD NOT DUPLICATE AN ERROR. CLEANED ELECTRICAL CONNECTORS.