Reliability Centered Maintenance and Jabiru

[Bruce Tuncks]

Mike Bush has convinced me that " time-based preventive maintenance is counterproductive, worthless, unnecessary, wasteful and incredibly costly", but I would like some ideas on how to use his methods with my Jabiru. He sure does not recommend no maintenance, but he says non-invasive stuff like oil analysis and engine data logger examination gives better reliability than our old-fashioned ways.

 

Mike Bush was asked about Jabiru engines at one of his seminars, and he responded that he only could claim expertise on Continentals and Lycomings.

 

So we are on our own here . I would like to have a recipe on how to do this sort of maintenance, specifically tailored to the Jabiru engine. But it will take more ideas than I can come up with.

 

 

[jetjr]

If the aircraft is LSA you have no choice but follow Jabiru manuals

 

Mike is mainly talking about timed replacements or intrusie and inspections. other makes have a lot of them. Jabiru dont have too many excepting flywheel bolts, rubber hoses, gear bolts and longer in life control cables.

 

Secondly, not having ago here, but few get to major tbo levels or beyond without work anyway.

 

His approach is that you necessay dissasembly causes more problems than it catches.

 

Monitoring all engine parameters and recording leakdowns provides more info for when a problem does come up and helps with action plans

 

 

[Mriya]

If the aircraft is LSA you have no choice but follow Jabiru manuals

Spot on JJ. Many people are unaware that they are obliged to perform all maintenance per the manufacturers schedule. I've seen aircraft with no logbook entries for 3-4 years and people saying that it was all ok because the aircraft is registered by RAAus, not CASA. All that had happened was a few undocumented oil changes.

 

I sympathise with Mike's thoughts re unnecessary invasive maintenance, however a good example of applying this is already possible using 'on condition' provisions for running engines past their TBO hrs or calendar time. This is done quite successfully when appropriate monitoring of compressions and metal in the oil is carried out.

 

However the manufacturer's schedule is designed to detect items before they actually break. There is no getting away from the need to inspect for developing issues, and unfortunately this sometimes requires disassembly for access. The key to conducting this safely is to be methodical and work within your capabilities in order to prevent errors during reassembly of said items.

 

 

[Bruce Tuncks]

"designed to detect items before they break" is an example of the fallacy that, while it is intuitive, has been shown to be incorrect.

 

"only 2% of components have failure rates that are primarily age-related, and 68% have failures that are infant mortality". This is so counter-intuitive that it took many years to discover and even now is often dismissed out of hand. But what if it is really correct?

 

 

[jetjr]

It is well known and understood, thats why most complicated products have a warranty and this is not considered the "life" of the product.

 

If it makes it past this point, its likely to go on to full life/hours.

 

Aviation is one of the few industries who still use timed replacements widely. Conditional monitoring is the way most operate expensive gear elsewhere these days.

 

You try to measure performance info and set limits for replacement or service. Yes you can determine when things will fail, vibrational monitoring. In our case logging EGT and CHT can lead to picking up problems. Annual leakdowns is another. The concept is to watch the changes in readings rather than set a strict limit. Make service decisions based on rate of change. Some fit monitoring gauges etc but very few takr this further to logging with aircraft. You also need a base of info to work from, we should but dont have this for Jabiru stuff.

 

Due to the risky outcomes of a failure in aircraft many limits are low or time based which equals cost and brings in post service failure issues.

 

In relation to Jabiru engines, they can and do have major unplanned breakages and many opt for preventative servicing.

 

Its hard to implement a conditional monitoring system on something that suffers premature (and largely unidentified) problems.

 

 

[Bruce Tuncks]

Nicely explained jetjr. I am in the process of setting up to measure digital EGT and CHT on all 4.

 

Your comment in vibrational monitoring sure got my attention since I have been thinking of doing just that. The gear is very cheap but the problem is, as you say, a lack of baseline info.

 

I reckon vibration measurement should pick up detonation for example. Can I bring this topic up again in a few months?

 

You say Jabiru have some premature breakages. In how many of these can you confidently eliminate bad fuel, bad operation ( allowing the engine to overheat, taking off with a bad exhaust valve, operating with a loose propeller) and other things that could be the cause ? For me, the answer is none that I know of for sure, although there has been a failed through-bolt with a good current operator, but he was not the first owner of the aircraft so there is some unknown history.

 

 

[jetjr]

Your right we dont really know the causes but do see symptoms. We dont even have basic data on these so how and what to monitor?

 

Vibration gear is out there no problems BUT cheap stuff isnt able to handle high temps found in air cooled engines and designed to watch one place ie a bearing set on a electric motor or pump. A whole engine is very noisy. Cant get detonation sensors working on air cooled engines Im told.

 

Smart avionics has a bluetooth model which could be setup to watch vibration all the time. You altenatively could run a check program every 25 hrs using a solid robe against set engine points and watch changes?

 

Dont like idea of doing this with prop swinging around.