As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) F/O`S OXYGEN MASK WHEN DONED, WEARER COULD NOT EXHALE WHEN BREATHING. ENGINEERING INVESTIGATION INDICATES THAT THE MASK EXHALE VALVE IS DEFECTIVE. MASK REPLACED. AIRCRAFT RETURNED TO SERVICE SATISFACTORY. MASK HAS BEEN RETURNED TO THE MANUFACTURER FOR REPAIR AND WITH A REQUEST FOR A STRIP REPORT. (TC NR 20070710002)