The oxygen line theory would explain a lot. I don't understand, in light of the Egyptair fire that gutted the cockpit, why AD 2012-13-05 gives the operator 18 months to replace the hoses. It seems it would be an emergency AD note with a 'replace before further flight' restriction. If the oxygen line does turn out to be a factor the airline will get tagged for not changing the line, Boeing will get tagged for installing the defective line it in the first place, and the FAA will get tagged for the 18 month compliance window. If I were a pilot on the 777 I would make extremely sure the lines had been changed out. Before further flight