Most of the stuff on airplanes is time limited. We don't wait for generators or pumps to fail. We replace it at a defined time point. Even the airplane itself has to have a C check eventually. We don't wait for stuff to fail in aviation before replacement. Well, in the past we didn't. I guess now it's OK to do that with the guy in the left seat.
OK Plectron, you make this point.
May I object that TBOs are revised when components reliability is proven to improve ?
Some aero-engines have seen their TBOs increased from 1.000 hrs to 2.000 hrs.
Other components no longer have TBOs. They are just "
inspected" and replaced/overhauled "
if necessary".
In 1959, age limit 60 for pilots probably made sense.
Not anymore in 2011 : pilot's "reliability", at age 60 (and above), have improved in 50 years.