As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE CLIMBING THROUGH FL 270 THE CABIN WAS CLIMBING WITH THE AIRCRAFT. A 10,000 FOOT WARNING ALERTED THE PILOT WHO THEN MADE AN EMERGENCY DECENT. AN INSPECTION REVEALED 2 PROBLEMS. THE REFERENCE LINE FOR THE OUTFLOW VALVE WAS MELTED AND THE FRESH AIR CHECK VALVE ON THE AFT PRESSURE WAS BEING HELD OPEN BY CORRODED BROKEN PIECES OF WIRE FROM THE FRESH AIR FLEX DUCT FROM THE NACA DUCT.