As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - FLT 247 - DURING CLIMB, THE AIRCRAFT BEGAN TO LOSE PRESSURIZATION AND THE AFT SERVICE DOOR WARNING LIGHT ILLUMINATED. THE AIRCRAFT RETURNED TO THE FIELD AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE AFT SERVICE DOOR NOT CLOSED PROPERLY CAUSED BY A BROKEN INTERLOCK SPRING. THE INTERLOCK SPRING WAS REPLACED AND DOOR OPERATION WAS NORMAL. (M)