As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW RECEIVED A NR 1 PACK FAIL MESSAGE AT FL 280. TRIED TO RESET WITH NO SUCCESS AND CABIN WOULD NOT HOLD PRESSURE. DECLARED AN EMERGENCY AND ELECTED TO RETURN TO DEPARTURE. LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED AND FOUND THE LT PACK FILTER CLOGGED. MAINTENANCE CLEANED FILTER IAW AMM AND OPS CHECKED GOOD. ACFT IS GOOD FOR SERVICE.