"O. Sami Saydjari" wrote
Where do they get TBO numbers from. I always assumed there was some
serious historical statistical date to back these up. Does anyone keep
these statistics? Perhaps A&Ps report such failures? Overhaul shops
maybe? I sure hope someone is tracking the information.

First off, nobody is tracking this information. The engine
manufacturers don't want it tracked - the statistics would reveal how
unreliable these engines really are. TBO's are usually about 2000
hours, but I don't actually know anyone with more than 2000 hours of
piston GA experience who has not had an engine failure.

Second, the TBO numbers are not MTBF numbers. In theory, they are
based on estimated corrosion and wear of critical components. For
example, improved lubricants have had a massive effect on TBO's
without the engine manufacturers doing anything. TBO is not how long
the engine is expected to go without failing catastrophically, but how
long it's expected to go before some components are no longer within
service limits. This can cause the oil consumption to be excessive,
rated power not to be delivered, etc.

Third, catastrophic engine failure is not generally the result of the
bottom end (camshaft, crankshaft, case) though it can happen. When it
does, it generally occurs earlier rather than later, unless of course
something ugly happens (like a prop strike). Usually such failures
are in the jugs (valves are most common, though I have seen engines
literally lose a jug) or the accessories.

Fourth, the serious engineering talent at places like TCM and Lycoming
has been gone for a long time. They don't offer top pay, interesting
work, or a minimally bureaucratic work environment, so they don't
attract the top engineering talent. Their TBO's are mostly a guess,
and a marketing rather than an engineering guess at that.

Fifth, the important TBO is not hourly but calendar. I don't often
see engines go much past the calendar TBO (usually 12-15 years)
without significant top end work. I've seen lots go past hourly TBO
when flown lots - as much as 3000 hours when flown 500 hours a year.

Michael