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912 Service interval - how to determine?

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3 years 6 months ago #11889 by dobbo
Sorry if this is an old chestnut, but I can't find it anywhere. How do you determine the 100-hour mark on a 912UL when the Hobbs meter is pressure-switched i.e just records flying hours? Do I just take the Hobbs reading, or should I also record my taxi-time and add that to it? After 100 hours flying there could be a 25 per cent discrepancy which don't sound right.

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3 years 6 months ago #11890 by RobSeaton
Replied by RobSeaton on topic 912 Service interval - how to determine?
FAA Definitions:
“Time in Service. With respect to maintenance time records, means the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing.”
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3 years 6 months ago #11893 by dobbo
Replied by dobbo on topic 912 Service interval - how to determine?
Thanks for replying Rob, That is indeed the FAA (and CASA, apparently) definition with which, I believe, Rotax complies in its' maintenance schedule timing. However Conair have told me that it is "Engine on time,regardless of load",so I'm still at a bit of a loss. Obviously,the oil-pressure Hobbs and the air-pressure Hobbs measure different times. I have the air pressure Hobbs, so it makes sense to be working on take-off to landing as you point out. Mustn't it???

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3 years 6 months ago #11894 by RobSeaton
Replied by RobSeaton on topic 912 Service interval - how to determine?
Rotax has a different opinion; they say all engine operating hours. See Line maintenance manual 05-10-00 sec 1.2 Operating hours. (I do not agree with this section and have been trying to convince Rotax to change it in accordance with FAA guidelines)
If you are in the UK then I am not familiar with your regulations but if they copied the FAA then I would for sure use flight time instead of engine run time.
My opinion: The engine does not wear appreciably during idle/run-up (it has no load, not working hard like in flight)
The engine is only one part of a simple aircraft; you cannot have one component dictating the maintenance schedule (until you get into big complicated aircraft: airliners, helicopters..)
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3 years 6 months ago #11895 by Conrad
Replied by Conrad on topic 912 Service interval - how to determine?
Rotax specify recording the operating hours of the 912 series a bit differently to convention. The details can be found in the Line Maintenance Manual section 05-10-00 paragraph 1.1

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3 years 6 months ago #11898 by dobbo
Replied by dobbo on topic 912 Service interval - how to determine?
Thanks for that, Conrad. Can't argue with black and white, throws a bit of a spanner in the works though. How do you determine engine-on time as per the Rotax definition if the Hobbs records only flying time?

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3 years 6 months ago #11899 by Conrad
Replied by Conrad on topic 912 Service interval - how to determine?
Ronald, Instruments like the Rotax Flydat provide engine total run time.
A solution might be to have your hobbs meter connected to the master/ignition switch or even have it switched by an oil pressure sensor. It really depends on the type of aircraft you are flying as to how easy it will be to fit something that will record engine run time.
Failing that you are going to have to revert to the old fashioned way of recording your engine start & stop times.
They way Rotax require the engine hours to be recorded is a bit unusual and I hope you fine a suitable solution.

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3 years 6 months ago #11900 by dobbo
Replied by dobbo on topic 912 Service interval - how to determine?
Conrad, a million thanks, you've been really helpful, especially in the light of foxbatpilot.com/2015/03/10/rotax-engine-...page-1/#comment-2462 . Thanks again.

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3 years 6 months ago #11901 by dobbo
Replied by dobbo on topic 912 Service interval - how to determine?

Rob Seaton wrote: Rotax has a different opinion; they say all engine operating hours. See Line maintenance manual 05-10-00 sec 1.2 Operating hours. (I do not agree with this section and have been trying to convince Rotax to change it in accordance with FAA guidelines)
If you are in the UK then I am not familiar with your regulations but if they copied the FAA then I would for sure use flight time instead of engine run time.
My opinion: The engine does not wear appreciably during idle/run-up (it has no load, not working hard like in flight)
The engine is only one part of a simple aircraft; you cannot have one component dictating the maintenance schedule (until you get into big complicated aircraft: airliners, helicopters..)


Rob, you are right, I'm in the UK, seems like we do things differently here :blink:

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3 years 6 months ago #11903 by Roger Lee
Replied by Roger Lee on topic 912 Service interval - how to determine?
This I'm sure is one of those discussions that has a fence that some fall on one side or the other. Is either right or wrong. Not to me, just a difference of opinion. One of those personal preference items.

I kind of fall on the other side of the fence. I prefer Hobbs time and anytime the engine is running. I just look at it that way because many have long idle times with low engine temps and any fuel that burns produces abrasive carbon and other contaminates regardless of rpm. So for me any run time is contaminating the oil and if using 100LL long low rpm times may cause more lead build up at those low rpms?

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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3 years 6 months ago #11904 by RobSeaton
Replied by RobSeaton on topic 912 Service interval - how to determine?
Scenario:
A busy flight school cannot ground an aircraft because the engine is due for its 100hr inspection at 98hrs (because of ground running engine for whatever reason), and then its grounded again at 100hrs when the airframe is due. Nor can they "give away" 2 hours and perform the 100hr check at 98hrs. It is a huge cost in a very challenging industry.
The FAA is correct: airtime is the only proper, consistent way to measure hours, in respect to maintenance intervals.
OK, most owners are not flying schools but here we have a simple rule that makes sense and works for most situations. Why not keep it consistent across all general aviation?

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3 years 6 months ago #11905 by Conrad
Replied by Conrad on topic 912 Service interval - how to determine?
Rob,
I agree with your sentiment, but Rotax (according to the Line Maintenance Manual anyway) require the hours to be recorded based on total run time for the 912/914 series. You as part of their distributor network might be able to influence a change to this or at least clarify the situation. Do you know what the official line is from the factory?
The info posted by Ronald suggests the factory may have had a change of mind but it hasn't reached the manuals.
foxbatpilot.com/2015/03/10/rotax-engine-...page-1/#comment-2462

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3 years 6 months ago - 3 years 6 months ago #11906 by Roger Lee
Replied by Roger Lee on topic 912 Service interval - how to determine?
Tell them to plan better. :lol:

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
Last edit: 3 years 6 months ago by Roger Lee.

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3 years 6 months ago - 3 years 6 months ago #11907 by dobbo
Replied by dobbo on topic 912 Service interval - how to determine?
Thanks to everyone for the input. Until someone persuades Rotax differently then it's "by the book". Manufacturers know their engines and that is good enough for me.
Last edit: 3 years 6 months ago by dobbo. Reason: contention

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3 years 6 months ago #11910 by RobSeaton
Replied by RobSeaton on topic 912 Service interval - how to determine?
No, its not about getting out of warranty. (Sorry conspiracy theorists, it is just not true :cheer: ). They do have the best interests of the engine in mind and have a good argument that when the engine is running there is some wear. Like Roger says.

We will/are trying to get this changed but for now the manual is like Conrad says.

But; the aircraft manufactures instructions always overrule the engine manufactures instructions so check to see if your OEM has their own maintenance checklist (most just reference the Rotax manual so those are out of luck)

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3 years 5 months ago #11982 by Russ_H
Replied by Russ_H on topic 912 Service interval - how to determine?

Ronald Dobson wrote: Thanks to everyone for the input. Until someone persuades Rotax differently then it's "by the book". Manufacturers know their engines and that is good enough for me.


I think that is the right choice Donald, after all, Rotax built your engine, not the FAA

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6 days 2 hours ago #22838 by NichollsJ
Replied by NichollsJ on topic 912 Service interval - how to determine?
This has already been posted by someone else but the Rotax 915 manual now has a note explaining acceptable timing methods. Hopefully this can be applied to other engines too - I do not know how to contact anyone int eh factory to ask!

DEFINITION OF TERMS
OPERATING HOURS
Definition All of the maintenance intervals, such as the 100 hr. inspection and the engine TBO, relate
to the number of operating hours of the engine.
General Note • In aviation there are different measurement methods used as an acceptable means to
record operating time elapsed.
• BRP-Rotax does not mandate a specific method to record time elapsed as a basis for
maintenance and overhaul intervals.
• BRP-Rotax therefore relies on common practice and defers to the aircraft original equipment
manufacturer and/or local regulations.
In order to prevent misunderstandings and to ensure safety, BRP-Rotax accepts any of
the following methods to record operating hours:
• mechanical hour meters such as an oil pressure switch, etc.
• electronic hour meters such as BRP-Rotax ECU, TCU, FlyDat, etc.
• "flight Hours" entered in the aircraft's Journey Log or Technical Log.
• operating hours determined by "Hobbs" or "Tach" time (if the aircraft does not have
Journey or Technical Log)
NOTE
Maintenance and overhaul intervals are always dictated by the relevant method
used.
NOTE
The planned inspections to be performed at certain intervals are based on experience
from long test runs and field observations. They are intended as precautionary
maintenance measures in order to ensure continued trouble-free operation of
the engine.

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