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jackwhickman

Rotax TBO Confusion

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I have a 2006 CTSW, Rotax 912ULS S/N  5.646.169 with 660 hours on the engine.  The original Line Maintenance Manual specified the TBO as 12 years, 1500 hours. The 12-year requirement has now run out.  However,  Service Bulletin SB-912-057UL  gives instruction for extending the TBO to 2000 hours, 15 years which doesn't look too onerous.   However, at the bottom of page 6, the Service Bulletin reads reads:

 

"Replacement of  a crankcase part no. 888364 (to S/N 27.811) through part no. 888368 or part no. 892654 (from S/N 06.0010) is required for TBO extension. 

Following engines are affected

912ULS from S/N 4,427.533 to 5.646.559"

 

My question is:  Does this mean what I think it means, that my entire crankcase has to be replaced to have the TBO extended?

 

If so what options does this leave me ----  replace entire crankcase, buy new engine or go experimental?

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Unless you are using the airplane for a commercial purpose, the TBO is advisory only; you are free to operate the engine "on condition".  That means you maintain the engine properly and monitor its condition through metrics like oil consumption, compression test results, spark plug condition, seal integrity, etc.  If it ain't broke, you don't have to fix or replace it. 

There are many Rotax 912s in the field with 3000+ hours on them with no issues.

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Go "on condition". I have a 2008 Remos in for a hose change and it has 2400+ hrs. on it. There is another friend of mine that has 2500 hrs. I know of people past 3000 hrs.

The TBO debate is in legal at the FAA for more guidance. My bet it will be a year before anything definitive comes out.

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4 hours ago, FlyingMonkey said:

Unless you are using the airplane for a commercial purpose, the TBO is advisory only; you are free to operate the engine "on condition".  That means you maintain the engine properly and monitor its condition through metrics like oil consumption, compression test results, spark plug condition, seal integrity, etc.  If it ain't broke, you don't have to fix or replace it. 

There are many Rotax 912s in the field with 3000+ hours on them with no issues.

My understanding is that even for commercial purposes in general TBO is not mandatory, but at a certain point commercial operators are more worried about liability.  

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That may be true Ben...I don’t have even a toe in the commercial pond, so I never paid much attention to the rules.  I just know for recreational use TBO is not mandatory.

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17 hours ago, Ben2k9 said:

My understanding is that even for commercial purposes in general TBO is not mandatory, but at a certain point commercial operators are more worried about liability.  

Anything that isn't part 91 requires folloeing manufacturer service bulletins, so TBO actually is required. However, providing the FSDO eith things such as oil abalysis and compressions will allow you to recieve a letter of authorization to exceed TBO by x hours, which then the process is repeated.

Any service bulletin compliance can be waived as long as you can provide evidence that it doesn't impact flight safety.

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I realize this topic gets beaten to death every couple of months with no definitive answer. It came up with our airplane recently and this was the response from an FAA source when taken to the Ankeny FSDO in Des Moines:

Robert,

 

In response to your question, “…are we in violation of any FAA regulation by continuing operation beyond TBO in this Light Sport aircraft…,” the answer is yes. Per a 2015 FAA legal interpretation, Keller:

 

The aircraft would not be airworthy if operated beyond TBO or outside the manufacturer's specified life limits. Section 21.181(a)(3)(ii) states that "a special airworthiness certificate in the light-sport category is effective as long as the aircraft conforms to its original configuration, except for those alterations performed in accordance with an applicable consensus standard and authorized by the aircraft's manufacturer or a person acceptable to the FAA." An aircraft that is operated after components have exceeded life limits specified in the manufacturer's maintenance manual or other procedures developed by a person acceptable to the FAA would not comply with § 21.181.

 

Option 2:  Aircraft previously issued a special airworthiness certificate in the light-sport category under § 21.190 may be eligible for an experimental certificate for operating an LSA under § 21.191(i)(3). These aircraft have previously been flight tested and are not required to have additional flight testing unless they have subsequent alterations to the aircraft that were not approved in writing by the LSA manufacturer and recorded in the aircraft records.

 

I hope this helps. Give us a call if you have any questions.

 

Best regards,

 

Patrick T. Blaskovich

Principal Maintenance Inspector

DSM FSDO/CE-01

3753 S.E. Convenience Blvd.

Ankeny, IA 50021

515-289-4835 (Direct)

515-289-3840 (Office)

He also made it clear that 'TBO' referred to the hours of and/or time in service of the engine of an LSA, as stated by the manufacturer, and attached the included files as reference.

F8130-6 AW Cert.pdf

keller - (2015) legal interpretation.pdf

FAA Order 8130.pdf

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The 'manufacturer' is the airframe manufacturer. LSAs are certificated as a whole unit, what a manufacturer chooses to install on that aircraft is up to them, and it is entirely on them to manage the airworthiness.

This is why you see flight design issuing safety directives for rotax components.

In the standard airworthiness world, aircraft are still certificated as a whole unit, but many of the components also have type certificate data sheets with limits, and ADs can be issued against components as they are under more scrutiny. Those also must be complied with.

The issue here is that the manufacturer, flight design, has not specified a time limit on the engine in their maintenance manual. If they did, this would have a lot more teeth. Rotax is NOT the 'manufacturer'. Flight design is.

My information comes from Edsel Ford when he was still at AFS 610.

The ASTM committee is also trying to put TBO requirements in the new versions of the consensus standard. If they succeed and it's accepted by the FAA, it will become next to impossible to get around it for aircraft built to the new standard (will not apply to older aircraft built to the older standard).

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He wasn't into the LSA main stream. This has been a major problem for many because of differing opinions from FSDO's and office staff in OK at the FAA. Too many conflicting views especially since they disbanded the LSA section. There is one person still there that knows all the LSA  better than anyone else. I got it right from him that it isn't illegal. It's still a big grey area.

It is a problem even for the FAA because they sent it to legal for interpretation 6 months ago because they couldn't agree and too much bad info when people called.. When I ask the top guy if anyone would be violated at this time he said no. Your guy's quote from above did not go into the sub-parts far enough. The the top guy worked with me he went way down into the sub-parts.

There are many aircraft out there well past 1500 or 2000 TBO. I have one in my shop right now with 2400+. One not too far away from me with 2500+.

Don't ask me what those are now because that was many months ago.

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Does anyone know why an engine reaches TBO based on years in service v engine hours. Mechanically, why are some 912 engines reaching TBO at 12 or 15 years?  Thanks, Tweeter 

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5 minutes ago, Tom Kinnear said:

Does anyone know why an engine reaches TBO based on years in service v engine hours. Mechanically, why are some 912 engines reaching TBO at 12 or 15 years?  Thanks, Tweeter 

The reason for the calendar month TBO is because sealants break down and seals dry out. The same kind of calendar month TBO is in place for Continental and Lycoming, but in the standard category world you are allowed to inspect based on condition. IMO, the same should apply to the LSA world.

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Some 912 engines reach TBO 1500/12 years and newer 912 engines reach TBO at 2000/15 years. It seems that sealants/seals would breakdown at the same rate over time.  One owner mentioned extending TBO from 12 years to 15 years by replacing the crankshaft. I assume that is because of the rubber components in the crankshaft are newer/improved? 

Bottom Line: Once an engine exceeds TBO based on time is there a safety issue i.e., a greatly increased potential for a catastrophic failure of the engine? 

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Actually the change for some engines is a simple as changing a spring and nut of the oil pressure relief valve. You have to realize that Rotax as a rule has been very conservative with overhaul times. As in service information is gathered they have made changes to the engine design, and lengthened the TBO.

To answer you question about risk of catastrophic failure, I would say there is no increased risk, at least that is my opinion. 

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The case can be made, and has been by respected maintenance authorities like Mike Busch, that a well-running and maintained engine past TBO will be more reliable than a brand new engine.  Improper break-in or just infant mortality of parts makes brand new engines fail occasionally.  I think reliability is a bell curve regarding hours, the highest failure rates are on brand new engines and engines that are *really* far past TBO.

BTW, Rotax had a contest a while back where they awarded a brand new 912iS engine to the owner with the highest time on a 912UL/ULS engine still in service with proper log documentation.  The winner was a flight school running a 912ULS with over 6000 hours on it.

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6 hours ago, FlyingMonkey said:

. . . . . Rotax had a contest a while back where they awarded a brand new 912iS engine to the owner with the highest time on a 912UL/ULS engine still in service with proper log documentation.  The winner was a flight school running a 912ULS with over 6000 hours on it.

By any standard, that is pretty impressive.

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1 hour ago, procharger said:

I wonder how school can  operate engine legally that far past TBO I plan to run mine

way past 2000hrs when time comes not that far away.

A flight school operates under the same rules that you operate under, unless you are experimental. That being said Rotax's hunt was world wide, the 6000 hour engine could have been in a different country with different rules.

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7 hours ago, Mike Koerner said:

Monkey,

Your bell won't chime. It's upside down with the clapper leaning against the inside.

What you describe is called a bathtub curve.

Mike Koerner

Yeah, it's an inverted bell curve.  But I didn't want to go into statistical analysis to get the point across.  If you are mapping failure rate, it's a bathtub curve; If you are mapping reliability, it's a bell curve.  Two ways of saying the same thing.

 

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My 2 cents worth on this: acknowledging all those who indeed know far more about the "nuts and bolts" of aviation then I do, is that guidance from the FAA in any court will carry FAR more weight in litigation in a court of law. Whether it be against your ticket, or even worse, liability damage from an accident or giving your insurance co. an 'angle' to be able to back out of coverage for an unfortunate event. That's why we went Experimental.

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