Kirstey, If indeed in 10 years time the aircraft is worth 12.000 (actual market value) and has a 6.000 engine fund, and you're still prepared to sell your 1/10th share for 1200, give me a call. In fact, please encourage all the other members to do likewise.
That means I pay 12.000 in total and get a 6000 engine fund thrown in for free. Sounds like a good deal to me.
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Think of this. If I buy your share of the aircraft, who becomes the owner of the engine fund? You're no longer the owner, since you've got nothing to do with the aircraft. As part of the transaction, you're selling your share in the engine fund to me. Because despite all the hoopla about deferred liability, there is a bank account somewhere with 6000 pounds in it. This bank account is owned by somebody, or has joint/shared ownership. And neither the money nor the bank cares whether that account is called an "engine fund" or something else. It's money, and it's owned by someone. So it's an asset. And you're selling it to me as part of me buying a share in the group.
If you want to do it real properly as a bookkeeper, what you need to do is deprecate the aircraft engine with each flying hour, and offset that depreciation with the formation of an engine fund.
Here's an example for your case, where I assume that the engine, zero-time is worth 10.000 and to get it overhauled or replaced at TBO costs 6000, and needs to be done after 1000 hours.
First, everybody in the group puts up 1600 UKP. Balance sheet
Debit (asset) side
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Money in the bank - 16.000 UKP
Credit (liability/private equity) side
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Private equity - 10 shares @ 1600 UKP = 16.000 UKP
Total assets: 16.000 UKP
The group buys an airplane:
Debit side
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One airframe- 6.000 UKP
One aircraft engine, 1000 hours to TBO - 10.000 UKP
(Split into two for bookkeeping reasons - because they depreciate differently)
Total assets: 16.000 UKP
Credit side
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Private equity - 10 shares @ 1600 UKP = 16.000 UKP
Now everybody starts flying and generally having fun. The engine overhaul will cost 6000 UKP after 1000 hours so for each flying hour they put 6 UKP in the engine fund. Here's what the balance looks like after 100 hours flying
Debit side
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One airframe @ 6000 UKP
One aircraft engine, 900 hours to TBO - 9400 UKP
One engine fund, stored in a bank account - 600 UKP
Total assets: 16.000 UKP
Credit side
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Private equity - 10 shares @ 1600 UKP = 16.000 UKP
See that the balance does not change? Your private equity is still worth 16.000 UKP, or 1600 per head.
Now the engine is totally run out. It did its 1000 hours and all that's left is a recyclable core which indeed happens to be worth 4000 UKP:
Debit side
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One airframe @ 6000 UKP
One aircraft engine, at TBO, recycle value - 4000 UKP
One engine fund, stored in a bank account - 6000 UKP
Total assets: 16.000 UKP
Credit side
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Private equity - 10 shares @ 1600 UKP = 16.000 UKP
The engine is overhauled for 6000 UKP:
Debit side
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One airframe @ 6000 UKP
One aircraft engine, 1000 hours to TBO, recycle value - 10000 UKP
One engine fund, depleted - 0 UKP
Total assets: 16.000 UKP
Credit side
====
Private equity - 10 shares @ 1600 UKP = 16.000 UKP
But now for the interesting bit. Suppose after 500 hours of flying someone in the group decides to sell his share. Here's the situation at that point in time:
Debit side
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One airframe @ 6000 UKP
One aircraft engine, 500 hours to TBO, recycle value - 7000 UKP
One engine fund, stored in a bank account - 3000 UKP
Total assets: 16.000 UKP
Credit side
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Private equity - 10 shares @ 1600 UKP = 16.000 UKP
As part of his pre-purchase survey, the aircraft is valued against current market value, taking into account that the engine is half-time. The surveyor finds that similar aircraft, in the current market, sell for 12.000 UKP, but also confirms that an engine with 500 hours left is still worth 7000 UKP if sold separately, so it's the airframe which has depreciated (or valued too high to begin with) and is now worth 5000 UKP. This information leaks to the group and they realise that their aircraft (more precisely the airframe) needs to be depreciated. So they rewrite the balance sheet and it now looks like this:
Debit side
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One airframe, now depreciated by 1000 UKP: 5000 UKP
One aircraft engine, 500 hours to TBO, recycle value - 7000 UKP
One engine fund, stored in a bank account - 3000 UKP
Total assets: 15.000 UKP
Credit side
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Private equity - 10 shares, nominal value 1600 UKP, now worth 15.000 UKP
So each owner now has been 'had' due to the depreciation for 1000 UKP. Nevertheless, a fair value for each share of the group is 1500 UKP: total assets minus debts (of which there aren't any) divided by number of shares. Now depending on the hurry of the seller and the buyer of the share, the actual share sale price as negotiated between the buyer and seller may be more, or less, than 1500 UKP. But 1500 UKP is what the negotiations should start with.
To sum it up: the shareholders are the owners of all the assets in the group, minus any debts that the group might have (which they don't in this example). An airframe is an asset, an engine is an asset, and money in the bank is an asset. If you buy or sell a share in the group, all the assets should be taken into account.