To respond to both Helvellyn (post 757) and SpacePhoenix (post 758) in one go!
Large commercial aircraft have a complete strip down every 6 years when the airframe is inspected, cracked parts repaired or replaced and all other flight critical components examined and replaced if necessary; it also has a repaint. If appropriate some components, avionics especially, may be updated. This is a very expensive procedure running into the millions, for a 747 it takes about 6 weeks. At the same time the plane is not earning any money.
Experience shows that it is economic to do this strip down three times, that is the last one will be done when the aircraft is about 18 years old. By the time the next strip down becomes due the plane will be 24 or 25 years old. By then improvements in operating economy because of better aerodynamics, structures, engines and avionics will mean that buying a new aeroplane after a quarter of a century is more advantageous than stripping down an existing one. There are few, if any, aircraft older than 24 or 25 flying in commercial service with any of the major airlines. It is not worth soldiering on with geriatric jets.
To transistors and similar. As I suggested in my earlier post the limit is not the number of operations per se. The limit is set by the chemical diffusion of the dopants in the semiconductors which define the p-n junctions, if the junctions drift or their performance decays the the device will move outside its designed performance limits. The rate of diffusion is set by a combination of temperature, time, materials and electric field strength. There is no set, immutable concept of max lifespan but obviously components will need to be replaced as their performance decays. So thats why I asked if the power electronics had been run too hot - in the context of the age of the power electronics they are middle aged.
It seems to me there must be other grounds for Eurostar to get rid of most of its Class 373s - and it is not because they were 'hammered'.
)
.
