Moderator, Iberia Airlines, Airport Lounges, and Ambassador, British Airways Executive Club
Join Date: Feb 2010
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The two prong adapters are needed for those airlines that separate out Left and Right into different lines and different plugs. BA has never used that (excluding occasional wet leases), so it's a useful adapter to have for frequent travellers to have in their HBO, but in the case of BA it's not needed. So the usual 3.5mm phone connector is all you need for BA. There is a second socket (which isn't 3.5mm) in some cabins, but that's used for the Active Noise Control channel, in other words for the noise-cancelling headphones and though there is sometimes electrical leakage from that channel into the audio signal, you can ignore that socket and work with the 3.5mm connector alone. That includes WT on BA's 777-300 aircraft.
I have - very occasionally - seen a snapped off connector in the socket, and on one occasion - out of boredom - I managed to extract the connector stump using the toothpick and olive oil off the CW meal tray. [Trivia of the day: the reason we've all ended up using 3.5mm jacks is thanks to the sheer popularity of Sony's Walkman products. Sony standardised on it, and now the 3.5mm is the Walkman's enduring legacy, culminating in YouTube videos of how to DIY retro-engineer 3.5mm jacks into Apple products].