lcloo
Captain
J6 was originally designed as a fighter, later development of this aircraft into a fighter trainer got its designation of JJ (Fighter Trainer), they retained the prefix J for Fighter and add another J for Trainer.Wasn't JJ historically used for trainer variants of fighters? Ie JJ-6
JL8 was designed from the start as a trainer, thus it couldn't be designated with a J prefix for Fighter, used of JL (Jiao Lian教练)was considered as more appropriate.
For export variants of trainers converted from fighter jets, the designation is FT (Fighter Trainer), as in FT-7, FTC-2000. K-8 is an exception as it is known as Karakorum-8 as it was a joint development between China and Pakistan.
So basically, used of JJ or JL, depends on the original design from the start, was it a fighter (converted to trainer later on), or a trainer.
2 seats fighter jets are still considered as fighters with J prefix if they retain full combat capabilites of single seat Fighter. And their design was for type conversion from one fighter jet to another figher jet (example pilot qualification conversion from J10A to J11B), rather than the normal pilot training. Thus you have J11B and J11BS.
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