Eh, you're gonna need more than one plane to hold a 135 cert.
If you get a contract from company A to haul freight for them and your plane goes tango uniform for one month for a engine overhaul, then company A finds someone else.
Nah, you charter it out for the month and make slightly less than you would using your own planes.
Or...the better way. Find a bunch of people that own different types of planes. You write the certificate (135), manage the planes (so you're always making $) and then if plane A goes down, you use plane B and so on.
Worst case scenario, you charter it out for a month. But it's not like you're going to all of a sudden go "oh snap, engine overhaul!!!". You'll normally see something like that coming. What is
bad is when the PMI stops in and say "hmm...here's a list of things that need corrected before the plane can fly" and it's 4 hours before departure.
If I were going to do another aviation business (and the thought has
crossed my mind), I'd manage. I'd want different sized turboprops, light smaller cabin jets and even cabin class piston twins and broker the living sh** out of them with pax, cargo, both...wouldn't matter. Anything to keep them in the air.
I'm tellin' ya...managing is where the $ is at. Why spend your money when you can spend someone else's?