What is the logic and system behind the two letters and three numbers of the aircraft of the Royal Airforce?
XX119 for exemple (being an Jaguar Gr.1) would recive (which it didn't) an complete new number would it have been updated to Gr.3 standard.
For Harriers and Tornado Gr.1/4 aircraft there have been examples were aircraft (the same hulls) received differend codes.
British military serials were allocated in sequence(with so-called blackout blocks used during the cold war in an effort to conceal the quantity of aircraft in use) until around the year 2000,when following USAF precidence serial numbers were allocated to highlight aircraft types( for example ZZ17x for C-17s) or units(for example ZK45x for the Beech 200s of 45(R)Sqn).
Normal serials are currently in the ZK range.Blackout blocks have stopped being used at the end of the cold war.Serials with numbers commencing in zero(for example Defender AL.2 ZH001) have been allocated when previously the number 101 would be the first serial allocated when a new letter prefix came into use(for example Sentry AEW.1 ZH101).
As far as I am aware,rebuilt airframes have never received new serials,wiht the exception of the Nimrod MRA.4.