There's nothing that can't be made (at a price).
But then there's the CAA/FAA paperwork and "product liablility" to deal with - which is why the "eternal warbird" will eventually be grounded.
Hence it's perfectly legal to fly with a 60 year old crankshaft made by relatively unskilled labour on a wobbly lathe (blessings be on both operator and lathe) because it was made in a Rolls Royce factory and has the 60 year old paperwork to prove it.
But highly skilled Fred Bloggs with his computer controlled lathe and modern steel just can't be trusted by the powers that be.
