noun
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.
複座機で飛行訓練を受ける。
I receive flight training in a two-seater airplane.
この複座機は軽量で操縦しやすい。
This two-seater aircraft is lightweight and easy to handle.
複座 is the noun meaning 'two seats' (in a vehicle), while 複座機 specifically refers to the aircraft itself.
Compound of 複 (ふく, 'double') + 座 (ざ, 'seat') + 機 (き, 'machine/aircraft'). A straightforward technical term.