Why do some airplane headphones have 2 Jacks instead of 1 everywhere else?

Question

Every time I go on a plane it is about a 50/50 chance between headphones with 1 jack or 2.

Why do some have 2 jacks? What is the function of it?

In: 21

Answer 1

Airlines used to take advantage of these fact that regular headphones only used one line in order to sell you adapters or headphones that use two lines in flight. Classis captive market cash grab.