I hadn’t thought of it. My first guess is because you don’t want a straight cord to get tangled up in your collective, but that’s just a guess. So I asked the question in my google box. I found this:
I’m supposed to be working right now, so I haven’t read past that post. It makes sense, though. When I started flying (fixed-wing) we didn’t use headsets. There was already a microphone jack. A pilot might use headphones (no mic.) and use the existing hand-held microphone. I know David Clark still offers headphones. Helicopters are very noisy. I flew, and would fly, a Cessna without a headset, but I wouldn’t want to fly a helicopter without one. Since headsets are the default, why not save a couple of ounces and have a single plug?
Only I have a different hypothesis. Helicopters were mainly used by the military early on, and many military aircraft used single plugs. Some pilots wore throat mics, which often/usually had a separate plug; or they used a ‘lollipop’ mic, which also had a separate plug. Many (leather or cloth) helmets though, had a small two-prong jack where the mic. could be plugged in, and had a single plug for the phones and the mic. The throat mic. could be plugged into it, or the helmet might be fitted with a boom mic., or the microphone would be incorporated into the oxygen mask. When fiberglass helmets came about, they had single cords for the phones and mic. By the time helicopters came into general military use, pilots wore hard helmets in them; so it’s natural that civilian helicopters would also use a single plug.
I think ‘legacy’ is a reasonable hypothesis for the use of single plugs in helicopters and dual plugs in airplanes. But what about the cords? Gomer Pylot opines that helicopter pilots spend a lot of time ‘with your head out the window’. When I was flying helicopters I didn’t stick my head out the door a lot, but I did do it. In fixed-wing I’m always looking around, but the space is more confined. It sounds reasonable. But from experience, I know that straight cords can get in the way. They have to go somewhere. I agree with Gomer Pylot that you don’t want your cord to get tangled in your collective, and a coiled cord is a good way to avoid that. I’m sure someone thought of it, and it may be ‘the’ reason for coiled cords. But again, I have a slightly different hypothesis. Headphone jacks in airplanes tend to be on the panel (usually on the lower left side for the pilot) or perhaps near the panel on the cockpit wall. In an airplane with a yoke, which is typical, a coiled cord would drape over the yoke or pull up on the left side of it. A straight cord hangs out of the way. The helicopters I’ve flown (Robinson R22, Schweizer 300) have the headphone jacks high on the rear bulkhead. Both the pilot’s and passenger’s straight cords would hang down over/into/around the collective. A coiled cord keeps the cord out of the way of the controls.
So one plug versus two plugs might be a legacy from the military format versus the civilian format, especially considering that civilian pilots used to generally not use headsets, and the coiled cord versus the straight cord might be due to the placement of the jacks and concern over unwanted interaction with the controls. These are complete guesses on my part, and I stand to be corrected.