The returnable lump sum is considered as a share in the aircraft thus making it an equity group, not non-equity.
What I suspect you have is a Beneficial Share. You can only expect your money back on demand if you haven't bought anything. If you have bought a percentage of the aircraft's value, then you must sell it back or give it back if your feeling generous. If you own a percentage of the value then the value of your share varies with the value of the aeroplane. It can go up or down. If you have secured a beneficial share then your share value remains fixed and you wouldn't share in any increase in value nor a loss.
This difference only matters, other than your money of course, if the aircraft is not maintained according to commercial use regulations when it can be rented out. If the aircraft is maintained only for private use it cannot therefore be rented for hire and reward and so you must hold a percentage of the value (equity) or a beneficial share to use it.