If you've got the Bose noise-cancelling headphones
You get the adaptor plugs shown above, included in the package. I've always been able to use mine - except on a couple of BA flights where the socket was so worn nothing worked - including BA's.
A couple of airlines (QF, I think) have a three prong plug. Here the third prong is to power the noise-cancelling. The Bose use a battery so the don't need power. The two prong adapter works here (power socket is a smaller size).