Do you mean used? Please be a little more specific, for example, What engines are used in aircraft, What instruments are used in aircraft.
Nitrogen is used in many aircraft tires.
Aircraft today are mainly used to carry passengers and cargo. Military aircraft are used as fighters, bombers, patrol aircraft and electronic warfare aircraft.
Steel is used to make aircraft springs.
Fighter aircraft are used to shoot down enemy aircraft.
No jet aircraft were used in WW1.
hellcats, helldivers
'Parked aircraft'.
Almost no natural products are used in building aircraft
Aluminium is used for most parts on most aircraft.
RV
Retractable wheels on aircraft are often called "landing gear", and some of the engine designs used in aircraft can contain a gear box. But gears as they look like in cars aren't used in aircraft.