I had this aircraft problem in my Virtual Airline. Basically I had set every schedules to one "virtual" aircraft that doesnt exist on fleet like A319TAM, A320TAM.
After that, when the pilot get this bid he has to reserve aircraft. On reserve system I just search on phpvms_aircraft, aircrafts that are on this airport.
And I had set on PirepData after accepted, set on phpvms_aircraft on column local the airport where has just landed.
This is my suggestion to you do. It's easy to make!