What was found
AIR TURNBACK -- DURING CRUISE CABIN PRESSURE WAS LOST. NO INDICATION OTHER THAN TAKEOFF WARNING HORN. REMOVED AND REPLACED OUTFLOW VALVE PER MM.
As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
AIR TURNBACK -- DURING CRUISE CABIN PRESSURE WAS LOST. NO INDICATION OTHER THAN TAKEOFF WARNING HORN. REMOVED AND REPLACED OUTFLOW VALVE PER MM.