In cash flow statement the one-time lease payment when ordering new/used planes is still under ops costs. Since that's what they basically are, just pre-paid. (unless you have other ideas for this?)
I think this is one of the items that throws off the income statement the most, by far, for airlines starting up and growing, while getting aircraft from Used Market. Also for airlines making large lease orders from New market. It is also an asset of significant value for pre-ordered aircraft, that may right now is completely hidden (sometimes for years, on new leased aircraft).
Therefore, I think there should be a balance sheet category (asset) pre-payments and also an expense category on the income statement for lease pre-payments, separate from regular lease payments.
So when an aircraft is leased, the amount paid would be reflected by increasing the pre-payment asset category, and also on lease pre-payment category (separate from normal leases).
It stays like this until the aircraft is delivered.
During the Day End calculation, when the lease expenses are charged, the system should first check if the aircraft is within the pre-payment period. If past, everything stays the same. If it is within the pre-payment period, the asset pre-payment category should be reduced by 1 day worth of lease.
The above is for leasing aircraft. The equivalent should also be there on the other side, when leasing out aircraft. A liability category for pre-payments received on Balance Sheet and pre-payment category in income section of the Income statement.
As far as the Income Statement, I think lease pre-payments and terminations are very similar. They are one time expenses, not regular operating expenses, and could possibly be merged.