What was found
FIRST OFFICERS OXYGEN MASK HEAD STRAP AIR HOSE IS DISCONNECTED FROM UNIT ON MASK, RENDERING MASK INOPERATIVE. SWAPPED 02 MASK WITH OBSERVER'S 02 MASK. DEFERRED OBSERVER'S MASK IAW MEL 35-10-1. ENTERED IN MM02. PLACARD INSTALLED. MAINTENANCE NOTIFIED. R & R THE OBSERVERS OXYGEN MASK IAW AMM 35-11-12. PERFORMED AN OPS TEST OF THE CREW MASK MIC IAW AMM TASK 23-51-00-710-801. ALSO, PERFORMED A LEAKAGE TEST IAW TASK 35-10-00-790-801. PERFORMED OPS TEST OF CREW OXYGEN SYSTEM IAW TASK 35-10-00. NO LEAKS FOUND. OPS CHECKS ARE GOOD. MM02 UPDATED. PLACARD REMOVED.