What was found
(AIRCRAFT NOT GROUNDED) (DISCREPANCY DISCOVERED DURING AIRCRAFT HEAVY MX VISIT) NRC 7000-0013: AT SEAT ROW 21ABC, 22ABC AND 29 ABC, O2 CONTAINER FAILED TO DEPLOY DURING OPERATIONAL TEST OF THE PASSENGER O2 SYSTEM. / AT SEAT ROW 21ABC,22ABC AND 29ABC, O2 CONTAINER REPLACED AND TESTED SERVICEABLE IAW AMM 35-21-41-400-001-A.