That $108 sounds a lot more reasonable. You need to be sure the partnership agreement spells out how the money is managed, and how the reserves are handled. Don't "invest" the reserves - short term CD's aren't a bad idea, but I know of one operation that played stocks and bonds with the reserves, and had an engine failure and a market downturn in the same quarter and the partners had to dig into their personal net worth to get the airplane fixed.
I STRONGLY suggest that a partnership airplane be owned by a holding company, not for liability concerns, but so that you can enforce multi-person-integrity on the finances, and partners can come and go without having to re-register the airplane. You can even take on partners of variable equity, though the operating rate stays the same. You can also spell out the standard of care for the airplane, meaning the duties the partners owe each other to keep the airplane nice and safe.
An annual review of the airplane's usage is a good idea, as you'll usually find that the more it's used, the more maintenance on consumables (tires, lights) there is, but overall your maintenance costs generally go down, so you may be able to reduce your hourly rate if the airplane is flown frequently.
