The right seat in the cockpit of an aircraft is the seat used by the co-pilot. The captain or pilot in command sits in the left seat.[1]
In some early aircraft, left turns were easier than right turns best of the direction of spin of the engine and propeller.[1][2] Hence it was advantageous for the pilot in command to sit on the left hand side. The tradition has been maintained to this day, with the co-pilot on the right hand side.