In ordinary flight outside controlled airspace, when two aircraft are approaching each other the aircraft on the right-hand side has right of way.
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Likewise with watercraft, I believe the starboard craft has right of way.
Also as with watercraft, if two vessels appear to each other as stationary, it’s because they’re on a collision course.
Regardless, an airplane has right-of-way over a helicopter. This is drilled into helicopter pilots from day 1.
I believe there is also a rule, for watercraft, that, if a collision threatens, between two vessels of radically different sizes, only the smaller craft maneuvers to avoid the collision -- the larger vessel maintains course, and speed. The thought is that the danger of collision is increased if you have two vessels playing Alphonse and Gaston, with each changing, and rechanging, course towards the other.
I don't know if aircraft have similar rules.