Al01/02 is the off callsign for the Belgian Alert Force. Like we had AK01/02 for the 32tfs, HH01/02 RAFG Phantoms, HG01/02 Germans, AJ 01/02 for Dutch Air Def Leeuwarden. After take off pilots hear by rt if it is a traning scramble or not. Training scr are often intercepts on overflying aircraft etc. But sometimes this flight is used for flyby’s or other special flights because they are always ready to go while the rest of the airforce is having weekend! The only thing is there must be a alternate airfield in case a diversion has to be made. Usaf airfields are mostly used during the weekend : Lakenheath, Ramstein etc
Some additions on Air Defence Callsigns. Nowadays most of QRA-flights are XX-01/02. A number of years ago some QRA's used 01/02 like 32TFS, AK01/02. Other QRA's used individual aircraft numbers when on alert like Leeuwarden, AJ01till 77. Every F16 has/had it's own number nothing to do with it's registration. RAFG Phantoms Wildenrath used ML as their callsign followed with their individual aircraft number. HH callsigns were used by Gilze Rijen, AG by Volkel, AM by Twenthe, HE by Hopsten. AL by KB, LH by Florennes and HG by Wittmund.
This all had to do with the Air Defence computer system. It only could read a number of letters in the labels and was an octal system hence 01 till 07 , 11 till 17 and so on till 77. 8 or 9 was impossible to insert, like with the transpondercodes.