Depreciation charged in the accounts will write-off the value of the machine to the P&L account over the economic life of the asset. In calculating your tax position, that depreciation is added back completely. You can claim capital allowances against the tax bill.
It then depends on whether your asset is "long-life" or not.
Most aircraft are considered "long-life" assets and excluded from the general equipment pool for capital allowances. There is an agreement with the airlines. However, for aircraft not covered by the airlines agreement see
CA23782 - Plant & Machinery Allowances (PMA): Long-life assets: Aircraft not within agreement
Accept that helicopters:
- in use for in excess of 1,000 hours per annum, or
- in use for more than 600 hours with 2,000 or more landings per annum, or
- which have a maximum take-off weight of less than 650kgs,
will not last for 25 years and will attract the rate of writing-down allowance for the main pool. For those in less intensive use below that figure you should approach any claims on the basis that the assets will only attract the rate for the special rate pool.
I believe that Robinsons are accepted as short-life assets due to the 12-year rebuild.