Hi, John.
This depends upon wether it is classed as a long life or short life asset, my Bell-47 is classed as a short life assest as it was under 100K (or so I was told by HMRC), so can be written off quickly (well, sort of)
Having said that I have spent around 35K on it with engine and gearbox O/H etc for the 50 or so hours I have flown it...
Kev.