Have any of you traveled on a Boeing 787 Dreamliner?
Does the onboard radio/TV connect with an adapter with two 3.5 mm jacks as in the picture below or does it have a conventional adapter?
The type of headphone plug used varies based on the individual airline, and occasionally even varies between planes on that airline.
There are generally 3 types of sockets used :
A normal 3.5mm headphone socket. Your normal headphones will plug into this without any problem.
A normal 3.5mm headphone socket, plus a smaller socket. These are used by noise-canceling headphones, with the smaller socket providing power to the headphones. Your normal headphones will plug into the 3.5mm socket without any problems - just leave the other socket empty.
Dual-3.5mm sockets, as per the image you've included. In general you can plug normal headphones into these sockets, however depending on the socket and your headphones you will hear either only mono sound (eg, the left sound channel, but in both ears), or sound in only one of your ears (eg, the left sound channel in one ear, and nothing in the other).
There used to be a 4th type which was dual-3.5mm sockets, plus a smaller power socket, but I haven't seen these used for many years.
The best option is to carry an adapter like the one shown with you. Some airlines will provide the adapter with their headphones - this is really intended just so that they can distribute the same headphones regardless of which plane type you are on, however there is nothing stopping you from using that adapter with your own headphones.
'Entertainment is provided by BA's fleet-wide entertainment system and Club World passengers get a 12.1-inch personal in-flight entertainment touchscreen with noise-cancelling headphones. They'll also get a UK/US/EU power socket, two USB sockets, and a Video RCA connection in order to use their own digital equipment to play back on the screen. Nice.'
Take a look at the website.
Hope this helped.
I was recently (2016) on two transatlantic flights, one a new 767 and another a new 787. These both use one (1) plug-in. I have Bose noise-cancelling earbuds for Apple. These fit and worked, but VERY poorly. They fit loose in the sockets and any kind of jiggling would cause me to lose sound in one channel. I don't have this problem with anything else or any other plane, and I don't know if the plugs for Apple are different or if there's something odd about the Boeing sockets. I've been searching to find if there's an adapter that could help for the future.