In article ,
Edward Todd wrote:

What is the deal with TBO? What do the regs say about it? I hear of
people running past it ... so is it not a legal issue? I wouldn't do it
for safety reasons ... but is it legal to run a 2000hour TBO engine up
to 5000 hours as long as it still passes the annual?


TBO is a reference established by the manufacturer for certification.
If you run an engine the way the factory did it, you will get the wear
as measured by the manufacturer.
In reality, there are many different ways to operate and engine. These
many different methods of operation will result in different wear
patterns. Some methods will allow you to go beyond TBO, others will
significantly reduce your TBO.
ie... Lycoming AEIO-540 in aerobatic service have a TBO of 1200 hours.
In the real world of aerobatic use, 600-700 is normal. When you go from
full throttle to idle with great rapidity in a 15 minute practice or
competition sequence, you are not operating the engine the same way the
factory did to establish the TBO.
Take that same engine and run it in a Cherokee Six, Cessna 210, or
Beech Bonanza, baby it, and you will go most likely go well beyond 1200
hours.