two-seater airplane; two-seater aircraft
Refers to an aircraft with two seats, typically a small plane or trainer. The term is straightforward and technical.
I receive flight training in a two-seater airplane.
This two-seater aircraft is lightweight and easy to handle.
Compound of 複 (ふく, 'double') + 座 (ざ, 'seat') + 機 (き, 'machine/aircraft'). A straightforward technical term.