It also depends on how any particular finance department wants to account for the maintenance; cash basis, accruals basis, current cost or historical cost? For an operator which has its own engineering facility, how are overheads absorped into the labour rate? Is VAT reclaimable (depends on the type of operation and where based)?
Skyhigh, whatever figure you want the average annual maintenance cost to be, I'm sure I can find a way of accounting for it!!
Cheers
Whirls