Is this a three pronged job with a triangle configuration and the top one smaller than the other two? You can see a picture on this review 5th picture down. If so the top hole in the socket looks like it is for powering the Noise Cancelling in the airline supplied headphones. This also prevents the headphones from working properly off the aircraft so a disincentive to pinch them. The other two holes are normally spaced a set distance apart and carry the left and right of the stereo signal. What you then need is a dual mono adapter to combine the L&R signals into your own headphone cable. This was the first one that popped up on Amazon many others are available and miy one came free with my headphones.