The way we handle it is simple: Each of the three owners owns 1/3 of the
airplane "as is". Each pays 1/3 of all costs except for fuel, which is
bought by the pilot using the plane. This works out well since we all use
the plane roughly the same number of hours/year. When we bought the plane,
the purchase price and all associated costs were split 3 ways. Each
co-owner is free to sell his "share", with the proviso that the purchaser
must be approved by the other two co-owners. If we decided to sell the plane
as a group, we would split all net proceeds.

--
-Elliott Drucker