When to overhaul

[Palle]

In the February 2012 issue of EAA Sport Aviation magazine, Mike Busch on page 52 discredit the TBO concept. Instead he recommends to use condition-monitoring tools to determine when it is time for overhaul. These tools include oil filter visual inspection and electron microscopy scanning, spectrographic oil analysis, digital engine monitor data analysis, borescope inspection, differential compression test, visual crankcase and cylinder inspection, oil consumption and oil pressure trend analysis. His reasoning is that engine life has little to do with engine hours in service but instead with corrosive exposure during periods of disuse and operator abuse such as cold starts and improper powerplant management.

 

Any comments on this theory?

[Roger Lee]

Hi Palle,

 

I agree that the TBO at 2000 hrs. may not be needed for the Rotax 912 and a condition inspection should be fine, but so long as FD says to follow the Rotax manual at this point you are locked in as an SLSA.

Now the interesting part is two fold. The FAA has been requested to look at the legality of the forced 2000 hr. TBO since the certified aircraft don't have to do it. The ruling should be out in Feb. some time. If they rule that Rotax can't make it mandatory then we are off the hook.

 

The other thing that some may do is wait until you get to 1950 hrs. and go ELSA which would effectively take you out of the mandatory arena too. 2000 hrs. will be a long time for most pilots unless you are using it at a flight school and that is a different story.

[Runtoeat]

Roger, this subject came up today while I was talking to my A&P who is "Heavy Rotax" certified. He said that he was talking to Lockwood and it appears that the trend now is for flight schools to remove and sell their CTLS engines with around 1500 hours and install new factory fresh engines instead of doing the 2000 hr. overhaul. Guess that there's a sufficient number of experimental builders who are buying the 1500 hour engines and paying good money for these. Acording to Lockwood, the money received from the sale of the used engines make it cheaper to repower with a new factory engine than doing the overhaul.Of course, if it turns out that we no longer are required to overhaul at 2000 hrs., I'm sure that there will be a lot us who will keep our engines well maintained and running past the 2000 hours.

[Roger Lee]

Hi Dick,

 

I have recommended this practice of selling a high time engine for years. It can be a less expensive way to go for a few thousand dollars and have a new engine. There are many Ultralight buyers out there. The schools are stuck with this, but we may or may not be which right now is a wait and see.

[Palle]

Hi Roger, Dick,

 

Thanks for your comments. Interesting that the FAA is looking into the Rotax mandatory TBO from a legal point of view. Didn't quite realize that certified airplanes don't have this strict rule and that for them TBO is suggestive rather than a mandate. Also didn't know that you could reclassify as an ELSA when TBO is reach without overhaul.

 

Palle

[Jeremy MacGregor]

I agree the mandated 2000hr TBO is a little strict. I've pulled apart a number of 912s that were well over the 2000hr TBO and while certain parts such as crank thrust bearings and pistons were either right at spec or just over, 95% of the engine measured out to serviceable tolerances. The highest time I've heard of is 3600hrs on a lower end, with 3 top overhauls down during the life of the engine. Rotax at one point was going to start a short block trade in program available only to the Service Centres which was suppose to cut down cost on overhauls for the end user. However, to my knowledge this hasn't gone into effect yet. I would highly recommend that anyone at or over the 1000hr mark should start there engine on an oil analysis. Every oil change can be a little excessive but every 100hrs will help you establish a good trend. These engines in particular because of the small diameter of the piston (only 84mm) tend to make using a boroscope almost useless. Unfortunately I found this out after spending $500 on a digital snap on one :-( There is no reason why any engine 2006 or newer should have a problem reaching 2000hrs without major work done, unless... You happen to burn close to 100% 100LL in which case a top end at 1500 may be needed to bring compression back up to the "like new" specs were all used to seeing even on relatively high time engines. Although if Rotax makes the new fuel injected engines released this spring retrofittable, I may pull my engine before 2000hrs just to upgrade to the latest and greatest :-)

[Jim Meade]

Hi Roger, Dick,

 

Thanks for your comments. Interesting that the FAA is looking into the Rotax mandatory TBO from a legal point of view. Didn't quite realize that certified airplanes don't have this strict rule and that for them TBO is suggestive rather than a mandate. Also didn't know that you could reclassify as an ELSA when TBO is reach without overhaul.

 

Palle

 

TBO is mandatory for standard certificated airplanes if they are used in Part 135 (charter and air taxi).

[Doug Hereford]

I haven't read Mike Busch's article, but I think I would agree in general with the statement that TBO may not always be the best guide to use when deciding to overhaul/ replace an engine or other aircraft component.

As for TBO's being legally mandatory: They are only mandatory when made so by specific regulatory language. Manufacturer's DO NOT currently have authority to make anyone do anything. Only our laws can do that. It doesn't matter whether Standard Airworthiness or SLSA.

TBO's can be made mandatory in SLSA by Operating Limitation (FAA Approved) or Safety Directive. They could also be mandatory by Airworthiness Directive in the case of a TC'd or other FAA Approved part installation on an SLSA aircraft.

SLSA manufacturers are required by law to tell us how to maintain and inspect their machine (ref part 21). Owners are required to have mx performed as required in part 91, and ensure that personnel follow those maintenance and inspection procedures (ref. Part 91).

To state a different way: SLSA aircraft manufacturers tell us how to perform maintenance, NOT when.