Mike Busch, Reliability Centered Maintenance and General Aviation

[Sluggo63]

I was reading through the "Mag Failure" thread and these two posts started me thinking about Mike Busch's books, especially Manifesto.

If you haven't read it, he advocates GA going towards a more Reliability Centered Maintenance (RCM) approach to maintaining aircraft much like what goes on at the airlines and military.

Basically, RCM says that preventative maintenance has a tendency to do more harm than good and that "Maintenance Induced Failures" are a real thing and is much more of a risk than flying a part until it's obvious that it needs replacement.

This topic is timely. Made me double check my own mags. They were way past 500hrs. Yanked them off for OH last night.

If I understand Busch's theory, I think he would ask "why would you pull both mags and send them for overhaul just because they were over 500 hours?" Were they giving you a problem? Were they failing a mag check? If they weren't, why mess with them?

Look at @Stingray Don's post.

The verdict is in. It looks like I got screwed.

The mag failed, and I need a complete rebuild. When I bought the plane in 2014, the right mag had 1,200 hours on it without ever being serviced. As part of the purchase agreement, I wanted the mag replaced which the seller agreed to do. The shop supposedly did the replacement. Well, my A&P said that one of the internal parts he hasn't even seen in the past 15 years and it did not appear to ever have been serviced. I doubt I have any recourse after 6 years, but I will consider my options.

The good news is that the plane should be done later today.

I mean, sure he got screwed because the previous owner didn't replace the mags like they promised they would, but apparently the mags lasted at least 15 years and over 1,200 hours (plus what ever he put on it in the last 6 years) without causing any problems.

What say you here about the RCM theory and doing unnecessary maintenance just based on time versus waiting until the part in question "tells you" it's time to be replaced?

 

[MuseChaser]

I don't know much, but my initial reaction would be that it would depend upon the part. There are some parts that I wouldn't particularly enjoy its telling me it's time to replace it while I was in the air. Maintenance-induced failure could, perhaps more correctly, be called Improperly-Done-Maintenance-Induced failure? Some things, like overhauling an engine solely because you've reached TBO, don't make much sense, while others, like changing your oil, filter, various air and static system filters, cleaning and testing spark plugs, wheel bearings, lubing fittings, ... all that stuff.. makes sense to do on a time schedule, and the .411/.413 checks every two years, blah blah blah.... lots of stuff is on a time schedule even though you may not see any warning signs that something's wrong, and it's a good idea. As with most things, I guess the answer is "it depends."

 

[Ron Stowell]

I'm not a fan. Given his theory, even if you can see metal particles in the oil, and the engine is still running making powe...so fly it until it completely fails is not the approach to maintenance.

 

[Radar Contact]

If I understand Busch's theory, I think he would ask "why would you pull both mags and send them for overhaul just because they were over 500 hours?"

Mags are one of his exceptions.

“Every 500 hours, the magnetos should come off the engine and go through a complete disassembly inspec- tion, lubrication, adjustment, and reassembly process generally referred to as a “500-hour IRAN”

https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2010-12_the-mag-check.pdf

 

[MauleSkinner]

Given the number of Timed-out functioning parts that we’ve replaced over the years with non-functioning parts from the OEM or other supplier, I think there might be something to the theory.

 

[Sluggo63]

Mags are one of his exceptions.

“Every 500 hours, the magnetos should come off the engine and go through a complete disassembly inspec- tion, lubrication, adjustment, and reassembly process generally referred to as a “500-hour IRAN”

https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2010-12_the-mag-check.pdf

Ha! I asked the question I wanted, and used the absolute worst example. Thanks for showing me that. Interesting... I guess my question still stands about RCM, but magnetos were a horrible example.

 

[Dana]

I'm not a fan. Given his theory, even if you can see metal particles in the oil, and the engine is still running making powe...so fly it until it completely fails is not the approach to maintenance.

Well, no. Metal particles in the oil is evidence that something has failed, or is failing, and thus needs to be addressed.

 

[Checkout_my_Six]

My master's degree is in RCM. He has lots of good stuff to say.

Let me add.....rather than run to failure, for most items it doesn't work in aviation, I'd rather have ways to "monitor" or have indicators that warn of impending failure. The method of determining that is to understand the "physics of failure". Based on those failure modes one can instrument and monitor to determine leading indicators to track or "monitor". Once that flag is tripped that's your sign to remove and repair the failure mode....often called "on condition" maintenance or "conditioned" monitoring.

DoD military systems and airlines have been doing this kind of maintenance for years. It improves availability (uptime) and reduces maintenance cost.

 

[3393RP]

My master's degree is in RCM. He has lots of good stuff to say.

Let me add.....rather than run to failure, for most items it doesn't work in aviation, I'd rather have ways to "monitor" or have indicators that warn of impending failure. The method of determining that is to understand the "physics of failure". Based on those failure modes one can instrument and monitor to determine leading indicators to track or "monitor". Once that flag is tripped that's your sign to remove and repair the failure mode....often called "on condition" maintenance or "conditioned" monitoring.

DoD military systems and airlines have been doing this kind of maintenance for years. It improves availability (uptime) and reduces maintenance cost.

The DoD and airlines have databases with millions of hours in them. They can easily establish on condition monitoring with that information.

I can't see a future scenario that has general aviation doing the same thing. The equipment is too diverse and the information is impossibly fragmented

 

[Tantalum]

*do you guys throw food away if it's one day past the date?

I don't.. the food does not know what day it is, if it smells okay and it looks okay and isn't grossly past the date then I eat it. And.. there's always a slight chance of getting food poisoning, you could be throwing away something perfectly good and instead replacing it with something that was already contaminated and getting sick from that..

 

[aterry1067]

Mags are one of his exceptions.

“Every 500 hours, the magnetos should come off the engine and go through a complete disassembly inspec- tion, lubrication, adjustment, and reassembly process generally referred to as a “500-hour IRAN”

https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2010-12_the-mag-check.pdf

I remember him saying that on a podcast, and it seemed a bit odd coming from him.

My thoughts, why not just send in one mag for the 500 hr IRAN, and run the second one to 1000? That way you'd only be paying for one mag every 500 hrs and would have at least one mag with less than 500 hrs at any given time.

 

[asicer]

*do you guys throw food away if it's one day past the date?

I don't.. the food does not know what day it is, if it smells okay and it looks okay and isn't grossly past the date then I eat it. And.. there's always a slight chance of getting food poisoning, you could be throwing away something perfectly good and instead replacing it with something that was already contaminated and getting sick from that..

Something like smoked salmon, no. For sashimi, probably. Either that or cook it.

 

[Checkout_my_Six]

The DoD and airlines have databases with millions of hours in them. They can easily establish on condition monitoring with that information.

I can't see a future scenario that has general aviation doing the same thing. The equipment is too diverse and the information is impossibly fragmented

Nah....there are enough similar components. It could be logged and tracked and analyzed. But, no one wants to sign up for that. Trust me....it's been discussed with the brain trust in the gummint and MITRE.

I wouldn't sign up for that...and that was expressed.....without some kind of relief from the regulator. But a third party like AOPA or EAA could effectively manage and disseminate the maintenance information to improve safety.

 

[Crashnburn]

I know vacuum pumps are going the way of the Dodo bird, but they still exist. My understanding is you replace them at 1/2 MTBF to avoid catastrophic failure in flight, especially in IMC.

 

[Hang 4]

RCM is usually based on something that predicts the failure (like @Checkout_my_Six said). An example of that would be putting a vibration sensor on a bearing housing in a steel mill. When the bearing starts to vibrate beyond a certain point, it's time to replace it. No time based change, only wear based. The challenge in aviation is what is the canary in the coal mine that gives you notice that something is about to fail. I think Mike B is not really talking RCM as much as the TBO times are pretty arbitrary and a well cared for engine can have a lot more hours post TBO. RCM becomes a handy buzz word to push back on the conventional wisdom.

 

[NoHeat]

Sensors do exist for some things, engines especially.

My engine is beyond TBO, and I’m planning to overhaul it on condition, not on time. Every oil change there’s no metal in the filter, and nothing worrisome in the oil analysis. In between oil changes there’s data from the engine monitor. Lots of ways to get advanced warning of failure. I’ll keep that engine until it gives me a reason not to.

For the battery, there’s also a sensor, the voltage meter. And I can request a load test at an annual. For a Gill at least, it gives you advanced warning.

The tires have a sensor, and that’s my eyes. For the brake pads, it’s the mechanic’s eyes. So there’s advanced warning, and we replace on condition.

Mags are the main thingI won’t do on condition. I’ll do them on time, at 500 hours. They do have sensors, RPM and the engine monitor, but I’m not sure if they’ll give me advanced warning.

 

[Chip Sylverne]

I know vacuum pumps are going the way of the Dodo bird, but they still exist. My understanding is you replace them at 1/2 MTBF to avoid catastrophic failure in flight, especially in IMC.

Or you could just inspect vane wear and replace the phenolic drive regularly like the Bendix SL recommends, as this is what generally fails.

 

[Daleandee]

Sensors do exist for some things, engines especially.

My engine is beyond TBO, and I’m planning to overhaul it on condition, not on time. Every oil change there’s no metal in the filter, and nothing worrisome in the oil analysis. In between oil changes there’s data from the engine monitor. Lots of ways to get advanced warning of failure. I’ll keep that engine until it gives me a reason not to.

This is mostly the way it works in the experimental aircraft world, especially if using a non-certified engine. Checking for metal in the filter, oil analysis, hot idle oil pressure, oil consumption or leaks, differential compression test numbers, borescope analysis, etc., are really good indicators of the health of the engine. Another great indicator is the owner/pilot of the aircraft. You should be in tune with the engine.

Before the first start of the day I like to pull through a few blades and feel the compression on the cylinders to see that they are all good & equal. Easy enough to feel a soft cylinder. If you know the engine well enough, when you find a soft cylinder when pulling the prop through ... you'll know which one it is ...