What was found
(CAN) DURING ROUTINE INSPECTION OF OXYGEN SYSTEM IN AFT CABIN SIDE WALL SUBMITTER FOUND THAT A SECTION OF PLASTIC OXYGEN LINE NEAR THE BACK OF THE CABIN WAS FOUND MELTED. IN ADDITION, A SMALL SPOT WAS ALSO FOUND AT MID CABIN ON LEFT SIDE. SUBMITTER SUSPECTS THAT MELTING WAS CAUSED BY RAPID OXIDIZATION OF UNKNOWN CONTAMINENT IN THE LINES. THIS COULD HAVE OCCURRED WITH PRESSURIZATION OF THE LINES DURING TEST OR EMERGENCY USE OF OXYGEN. ALL PLASTIC LINES TO BE REPLACED.