I am not completely positive about the new configurations though in the old there were two jacks as well. Unlike some of the other airlines where one jacks is left and the other is right for stereo audio, on UA one was a normal 3.5 jack and the other was a special power jack for their proprietary NC headphones in F/C on int'l routes. If you had your own NC they would work fine with just plugging into the standard jack.