I'm flying this Friday again and can't find my two-to-one 3.5 mm jack adapter and I was wondering why did they decided to go this way?

One like this:

I'm talking about these

I know why they were using the two prongs, to avoid of theft of the airline distributed headphones. But why not use two regular jacks and just switch the channels on the second one? This way everybody could use his own headphones.

  • 1
    Two questions. You might want to split them up.
    – MastaBaba
    Sep 20, 2015 at 19:32
  • "But why not use two regular jacks and just switch the channels on the second one?" I am not sure I completely understand what you are suggesting by this. But depending on how it was done, it might have meant that someone could use stolen airline headphones with regular equipment just by cutting off one of the two prongs. Sep 20, 2015 at 19:36
  • I'm afraid the answer is actually a lot simpler - the double - jack is a relic of the past, from a time where most people did not own headphones. There was no motivation to standardize it. Sep 20, 2015 at 20:25
  • 2
    It's mostly historical I suppose because I see fewer and fewer of these. Most my recent flights (80% at least) had standard jacks.
    – Itai
    Sep 20, 2015 at 23:36
  • 1
    See also aviation.stackexchange.com/questions/13154/…
    – Relaxed
    Sep 21, 2015 at 21:10

5 Answers 5


I'll speculate on your main question: Not only did the non-standard jacks mean that the airline's equipment would be useless outside of the airplane, it also meant you had to use their equipment if you wanted to listen to audio. Meaning, the airline could also charge you for it.

  • I totally forgot that this was the case back in the days... I guess that was the reason. Thanks
    – TS.
    Sep 22, 2015 at 11:34

I can only assume it was to prevent people from stealing their headphones. In response to your second question, I have often used my own headphones on planes that have the two jacks, with mixed results.

Most of the time you only get one audio channel when you do (as you might expect), which means you only hear out of one ear. This typically does not bother me.

Other times, if you pull out the jack slightly, you can get sound out of both ears. Its nice when this happens, although its sometimes a little tricky to keep the jack out slightly (it tends to fall out).


The reason was compatibility with piped sound sockets in older planes.

During the transition from piped to wired sound, the spacing between left and right channels was maintained as it suited the metal template in the individual passengers consoles


Well, as for "why", others have answered nicely. If you wanted to get around it without using their equipment, you could get a Y-cable in configuration 3.5 TRS F -- 2x3.5 TS M. I tried looking for it online, it seems to be uncommon, so you can either use two cables/adaptors that are available in the music stores (for instance 3.5 TRS M -- 2x3.5 TS M and 3.5 TRS F -- 3.5 TRS F), or solder one yourself.

Explanation to the vocabulary:

Your headphones have a stereo male jack, which is 3.5 TRS M. It fits into a female 3.5 TRS F. The mount in the place is two mono female outlets, which is 2x3.5 TS F, and 2x3.5 TS M fits in them. So, you need a cable with 3.5 TRS F -- 2x3.5 TS M, or a combination of cables that give you this configuration. This is exactly what you show in the picture, however, there the two mono jacks are in a fixed distance, if you use cables, you get variable distance, hence less troubles.

  • 1
    your explanation is no less confusing than the original :) Sep 21, 2015 at 21:40
  • @pocketfullofcheese I'll try to add pictures.
    – yo'
    Sep 22, 2015 at 6:15

On some aircraft the second jack is used to provide electrical power for noise cancelling headphones. On most of the aircraft I've been on recently, the 3.5 mm jack is the norm. The two pronged configuration, with one prong for each stereo channel, is becoming uncommon in Europe and North/South America.

  • But then the jacks would be TRS (at least the audio one), and not TS, see wiki.
    – yo'
    Sep 21, 2015 at 17:38

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