I think you use the MTBF approach to aircraft systems breaking, is it possible to do that on a curve? the more hours on a system the higher the probability, instead of a linear probability? I don't know the ins and outs of that, but seems like it would make sense. It's 'possible' for a part with only 10 hours to break, but much more likely, I'd think, with 10,000 hours on it. Then you could have the 'age' of the aircraft be the starting point on that curve, not the same as A2A, but similar?