I am seeing some airlines with 9 or greater fleet types.
At what point does adding a fleet type simply become too expensive?
I wouldn't add a fleet type until having at least 30 aircraft all of one type. Keeping a very strong fleet and engine commonality is a key to success. By experience I tried running short/medium haul aircraft, then at about 15 got bored of that type of expansion (or did not want to risk against bigger airlines when i joined late) and went on to longhaul, adding another fleet type and bankrupting shortly after the decision every time.
During my latest incarnation of Jet Italy in JA, I worked up a fleet of 60 aircraft sticking to only one fleet type, before only recently adding another fleet type without many issues. Needless to say in the meantime all those rapidly expanding 200+ aircraft airlines with more fleet types than routes went bust.
It really depends. If you have no competition, then potentially any number of fleets is ok. I mean, your profit margin would be so high that it would off set the costs of having too many aircraft type.
Ari (Sundaypilot) tested just how far you can take fleet common in beta. Ask him about his ventures. If I recall correctly, he at one point flew every type of aircraft alvb in the game.... while still making somewhat of a profit.
Now, flip the situation around, if you have heavy competition (50%+ of your routes flooded), then I would say 7 or more fleets would start to put a dent in your profit margin. Or at least leave you open to sudden changes ( 9/11 style pax drop or fuel spikes)
Again, its all relative to one's situation.
Talentz
I do recall after 3-4 aircraft types, your fleet commonality costs double...
I can confirm that. After my 4th type, commonality coasts went up by roughly 40%
so, should they double again when you hit 9?
Probably....