Mike
It transpires we're probably both right.
Your example - owner who buys an aircraft outright and then decides to sell a share. In that case yes - add the representative amount of the fund to the share value if you have added that amount of cash to the fund, without putting the time on the engine.
My example - existing syndicate, say 5 shares (for example) which has built up an engine fund through use. 1 shareholder decides to sell his share. His share is worth market value - NOT market value plus what they've put into the engine fund because they've paid for their use of the aircraft and engine in the hourly rate. In that scenario the engine fund is ringfenced.
Make sense now?