dstclair wrote:Out of curiosity, why replace your engine at 2000 hrs?
Dave, that's probably an excellent topic for its own thread, but I'll start with a response here.
Traditionally, TBO has always been advisory, not regulatory. An engine was replaced or rebuilt on condition. One keeps tabs of oil consumption, cylinder compression history, oil spectrographic analysis results, and perhaps frequent borescope inspections as the engine approaches TBO, and then makes an informed decision as to whether the engine is likely to fail between now and the next condition inspection. It's a gamble, but most people win at this game.
Initally, the SLSA universe followed the same replace-on-condition attitude. Then, engine and airframe manufacturers started writing life limits into their maintenance manuals and operating instructions. It was controversial whether these limits could be enforced, so somebody asked FAA Legal Dep't for a letter of interpretation.
<rant>BIG MISTAKE! Never ask FAA for an opinion if there's a chance you won't like their answer!</rant>
So, here's what FAA published. In a letter dated July 10, 2015 to Terrence K. Keller, Jr., Lorelei A. Peter, FAA Assistant Chief Counsel, Regulations Division, stated:
The aircraft would not be airworthy if operated beyond TBO or outside the manufacturerʹs specified life limits.
Pretty clear, no? But this is in direct contradiction with an earlier letter from the same Ms. Peter dated August 21, 2013 to Charles Willette of Dodge Center Aviation, LLC, in which she stated:
The intervals specified in maintenance manuals for S‐LSA, therefore, are not per se mandatory. Consequently, a maintenance provider may develop an alternative that is acceptable to the FAA and maintain an S‐LSA in accordance with those provisions.
Waters now muddied!
The most conservative course of action would be to assume that the more recent interpretation takes precedence over the earlier one. But our friend, master mechanic Mike Busch of Savvy Aircraft Maintenance, has recently asked for clarification. In a letter to that same FAA attorney, he wrote:
Clearly Willette and Keller cannot both be correct. I am requesting a definitive interpretation of
which of these two interpretations the owner or operator of an S‐LSA may rely upon.
These contradictory interpretations have created considerable confusion in the S‐LSA
community. In the past, this confusion has been largely academic because up until now few SLSAs
have been in service long enough for TBO to be an issue. However, a definitive resolution
of this question has now become time‐critical, because it is now 12 years since the S‐LSA rule
was adopted in 2004, and roughly 80% of the S‐LSA fleet is powered by Rotax 900‐series
engines for which the published TBO is 12 calendar years or 2,000 hours, whichever comes first.
Don't hold your breath for an answer from FAA, but if your engine is approaching 2000 (or whatever its published TBO is), you might consider an engine replacement. Especially
if your plane is in commercial service, where lawsuits and liability issues are pervasive.