What was found
FLIGHT 5119 DURING CRUISE FLIGHT CABIN ALTITUDE WAS INCREASING, AIRCRAFT RETURNED TO THE FIELD. REPLACED THE LEFT FUSELAGE SUPPLY (Y) DUCT.
As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
FLIGHT 5119 DURING CRUISE FLIGHT CABIN ALTITUDE WAS INCREASING, AIRCRAFT RETURNED TO THE FIELD. REPLACED THE LEFT FUSELAGE SUPPLY (Y) DUCT.