On the subject of A300 pitch trim systems.
Had a situation one night where one of the pitch trim systems was inop. and had been deferred IAW the MEL for 24 hours, the previous day.
The spares were not available to repair the system but the MEL allowed both systems to be inop for 7 days, so maintenance pulled and tagged the circuit breakers for the other system leaving us with no autopilot and only manual pitch trim. We were going to Cairo from Stansted, (about 5 hours). The captain said, "No Way". I asked which system was the good one and cut the ties on the CBs and reset them. Off we went.
We never got an answer as to why one system could be inop for 24 hours but both could be inop for 7 days.
(The MEL times may be slightly wrong but the gist of the event is as above)
Dixi.