- JAA Joint Aviation Authorities.
- JAR Joint Aviation Requirements, agreed by all major EC countries (JAR 25 equivalent to FAR Pt 25).
- JAR-VLA JAR classification for Very Light Aircraft (MTOW limit of 750 kg; 1,653 lb).
- JASDF Japan Air Self-Defence Force.
- JATO Jet-assisted take-off (actually means rocket-assisted).
- JCAB Japan Civil Airworthiness Board.
- JDA Japan Defence Agency.
- JGSDF Japan Ground Self-Defence Force.
- JMSA Japan Maritime Safety Agency.
- JMSDF Japan Maritime Self-Defence Force.
- joined wing Tandem wing layout in which forward and aft wings are swept so that the outer sections meet.
- JPATS Joint Primary Aircraft Training System (Beech T-6A Texan II).
- JSC Joint stock company.
- JSF Joint Strike Fighter.
- J-STARS US Air Force/Navy Joint Surveillance and Target Attack Radar System in Northrop Grumman E-8C.
- JTIDS Joint Tactical Information Distribution System (NATO Link 16).
- Junkers aileron Control surface (sometimes flaperon) suspended from mountings to the rear of wing trailing edge.
