On Jul 6, 1:07*am, Chris Rollings wrote:
I think you may find it's a manufacturere stipulated thing (at least in
some cases), like a TBO on engines in powered airplanes.


If it were just like TBO for engines in airplanes in would *not* be
mandatory. There is no legal requirement to do anything at TBO for
an airplane operated under Part 91. Many engines run well long past
TBO and far too many fail shortly after being overhauled.

Andy