I have suggested this before and I’m gonna suggest it again
Convert to cargo
I’ll reiterate the details
Once a aircraft reachs a certain point in it’s operation life (varying by aircraft, such as S-200 Hours, M-400 hours, L-700 hours, X-1000 hours, probably much shorter though, this is just an example)
The only aircraft able to do this would be ones with cargo versions currently available in game, such as the at76F going into the at75F, A332 into the F, possibly the A321F in the future
The would be an incentive to do this as well, such as a higher profit margin from the aircraft, or more rewards (xp or sp), however to convert to the aircraft you would need to spend the GP to do so, 1 for S, 2 for M, 3 for L, and 4 for X
Of course with many previous systems I mentioned in the original post being reworked, it is different than the original suggestion, but I think this way it could work