A good place to start looking at longevity is the Slingsby T-3. It is
probably the one aircraft out there that is really accumulating hours
at a rate with reliable and exacting maintenance standards, that will
give you a good idea. So far it has been a big bust in the training
program for the USAF. It is the only aircraft that I have ever seen
that has a structural temperature limitation. If the structure is over
a certain surface temp, it is prohibited from flight due to structural
degredation at the elevated temp. With the big engine, it is extremely
temp sensitive under the cowling and has what appears to be massive
vapor locking problems despite using multiple fuel pumps. The problems
with the a/c power and structure have become so problematical, that
the USAF grounded the fleet and will probably destroy the a/c rather
than let them get into civilian hands. I know it's only one aircraft,
but the design is certified at a minimum to FAR 23 standards.

What is interesting, is the a/c that are built to the same TC, and
using the smaller engines so far don't have the same problems. Even
those that are in military training programs outside the USAF don't
have the same fuel and structure problems that I've been able to find.

Craig C.