The importance of doing routine inspections

[Ted]

People who know me know that I'm a stickler for keeping after maintenance items on any aircraft I'm in charge of, focusing on the required things and then working on nice additions. Over the past two years, my Aztec has improved quite a bit from the state that its previous owner had left it in, mainly just by repairing things as they come along and then every time we have it in for maintenance do a few other "nice to have" items that weren't required, but have combined helped to turn the plane into a pretty nice example of an Aztec. It's made a big difference, even if the paint job is still ugly.

Given how the Aztec is set up, I do need to perform 100-hour inspections on it. However, my mechanic recommends doing them even if you aren't required to, because as he puts it, "You always find something that you wouldn't want to let go for longer." Given the fact that every time through the 100-hour we have found things that should be fixed, I'm inclined to agree with him.

This time, we found a major problem, as opposed to the minor problems we typically find. The right side motor mount was cracked. The break seems to have been very recent, my guess is it occurred on my last flight. According to the engine mount overhaul shop I'm having fix it, the place it cracked is where all Aztec mounts tend to crack, and they have an approved reinforcement action that they perform to prevent the problem from reoccurring. The mount has been sent off and will be returned hopefully in about a week or so, then the plane put back together. Unfortunately, the Aztec design is not a very nice one with respect to the engine mounts, so the plane is pretty well torn apart.

A number of people I've talked to seem to think that 100-hour inspections for personal aircraft flown more than 100 hours per year are a waste of money. In my experience, I would say that's not correct. Most of the time, you won't find anything major, but you will find something minor. Those few times you find something major, you'll be glad you found it on the ground and not in the air. I would not have been happy to discover this issue with a plane full of dogs. While you could say it should have been discovered during an oil change, this particular joint is burried deep enough that it quite likely would have been overlooked.

My mechanic called me up, telling me he found something really bad. I said "No, this is really good. Really bad would've been the engine falling off in flight."

 

[steingar]

I totally envy you. My aircraft gets a 100 hour inspection once a year. I wish I had the opportunity to do one more frequently.

 

[Ted]

I totally envy you. My aircraft gets a 100 hour inspection once a year. I wish I had the opportunity to do one more frequently.

Compared to some aircraft I know, yours is fortunate. It's sad to see the ones sit on the ramp that get 5 hours a year, if they're lucky.

 

[steingar]

Most aircraft will never see a wings off restoration in their lifetime. The Free Bird is indeed a fortunate aircraft.

 

[Jaybird180]

This time, we found a major problem, as opposed to the minor problems we typically find. The right side motor mount was cracked.
View attachment 21723

Holy Cow Batman

 

[Tom-D]

I have a Aztec owner here at OKH that removed his fuel selector valve 5 years ago, and the aircraft sat out side since then, no covers or any thing, last week he asked If I would do an annual and get it going again.

He insists that he do all the wrench bending to repair any thing I find. I told him to remove both props and engines and send them for over haul, He mumbled some thing I think was a bad thing and walked away.

 

[Fearless Tower]

Uh, Ted.....that's not a crack....it's a FRACTURE!

Holy Cow Batman is right....glad the inspection paid off.

 

[Ted]

I have a Aztec owner here at OKH that removed his fuel selector valve 5 years ago, and the aircraft sat out side since then, no covers or any thing, last week he asked If I would do an annual and get it going again.

He insists that he do all the wrench bending to repair any thing I find. I told him to remove both props and engines and send them for over haul, He mumbled some thing I think was a bad thing and walked away.

Your assessment sounds accurate. There's a Baron 56TC sitting outside at one of the airports I frequent. Been there for years. The guy insists the engines have been pickled and he can have it fired up and flying in an afternoon.

What a waste of a plane. I know the 56TC had some weird engines, but a plane after my own heart. I'd still love one.

Uh, Ted.....that's not a crack....it's a FRACTURE!

Holy Cow Batman is right....glad the inspection paid off.

This is the most major problem we've ever found on the plane. There have always been minor problems, but then again I've yet to see an aircraft without minor problems. This is why frequent inspections are a good thing.

 

[SCCutler]

Oh My.

---

As I said to the IA who just finished my annual, "the only thing worse than finding something wrong during the annual inspection, is not finding it." He was acting apologetic about finding discrepancies.

 

[Gary]

WOW! That is definately a problem! Interesting that you did not notice any major change in vibration, sound or other charateristics. Guess those Aztec's are pretty strong. Does it appear to be internal corrosion or metal fatigue?

Gary

 

[wabower]

Your assessment sounds accurate. There's a Baron 56TC sitting outside at one of the airports I frequent. Been there for years. The guy insists the engines have been pickled and he can have it fired up and flying in an afternoon.

He's probably right. But for how long?

 

[Ted]

WOW! That is definately a problem! Interesting that you did not notice any major change in vibration, sound or other charateristics. Guess those Aztec's are pretty strong. Does it appear to be internal corrosion or metal fatigue?

There was no indication of a problem from vibration or anything else, which is why failures like this can go undetected for a long while. As you'd expect, the mount is designed to be strong, but also there is definitely enough strength in there to allow for some failures without a catastrophic failure.

I didn't look closely enough at the break to say whether it was corrosion or metal fatigue, but I'm pretty sure it's the latter. As I said, the overhaul shop said this was an extremely common location for Aztec mounts to break, so there is probably something about the design that induces higher stress in that particular location.

He's probably right. But for how long?

Just long enough to get to the scene of the crash would be my guess.

 

[AdamZ]

Ted,

1) I am particularly happy that the engine did not fall off and plumet to earth with you in the plane and following shortly there after and ending up in a fiery ball of dog poop.

2) Since this is a common failure and it seems to be metal fatigue AND it appears that it happened recently would it be prudent to replace or reinforce the other engine mount at this time as well? Why wait for it to fail?

3) A little JB Weld will fix anything up :wink2:

 

[steingar]

The Free Bird actually sports reinforced engine mounts.

 

[Sam D]

If you electively have a 100 hour inspection performed, do you have it documented as an annual? I don't know if there is a big cost with the IA sign-off. But it would seem that, if you flew 150 hours per year, it might make more sense to have 3 inspections over two years instead of 4.

 

[Ted]

Ted,

1) I am particularly happy that the engine did not fall off and plumet to earth with you in the plane and following shortly there after and ending up in a fiery ball of dog poop.

Usually there is no dog poop involved, but I suspect that such an event would precipitate the occurrence of some.

2) Since this is a common failure and it seems to be metal fatigue AND it appears that it happened recently would it be prudent to replace or reinforce the other engine mount at this time as well? Why wait for it to fail?

Part of it is because pulling the mount out is a royal pain to do. It involves removing the engine, drilling out the rivets on the firewall, removing the firewall, then removing the mount, and all the disconnecting and reconnecting that goes along with that. The other part is that "common failure" doesn't mean "happens to every unit on a regular basis." For example, my mechanic, his partner in crime, and another mechanic friend of mine (all of whom have decades of experience) had never seen an Aztec mount crack at all. The overhaul shop sees a higher volume since, well, that's their job. So it makes sense that they can say "Oh, that's where Aztec mounts break."

My intention is to have the left mount removed and have the job done when I have to pull the engine off anyway, for example at overhaul, now that I know about this.

3) A little JB Weld will fix anything up :wink2:

Do you have an FAA PMA for that?

 

[Ted]

If you electively have a 100 hour inspection performed, do you have it documented as an annual? I don't know if there is a big cost with the IA sign-off. But it would seem that, if you flew 150 hours per year, it might make more sense to have 3 inspections over two years instead of 4.

Yes, that's what we do. One of my friends who used to fly his Mooney about 150 hours per year did the same thing - did an "annual" every 100 hours, which came out to be about 8-9 months typically.

 

[TMetzinger]

Ted,

1) I am particularly happy that the engine did not fall off and plumet to earth with you in the plane and following shortly there after and ending up in a fiery ball of dog poop.

Hmm have to change the acronym...
UWOF = Upsidedown in Weeds On Fire

Just for Ted...
WOOFED - Wing Over On Fire Eating Dogpoop. And it even fits his mission!

 

[gismo]

Holy Cow Batman

Nothing a little bit of duct tape couldn't fix.

 

[Fearless Tower]

Nothing a little bit of duct tape couldn't fix.

This isn't an aviation maintenance thing, but that reminds me of a problem I once had when I was Chief Engineer on a Navy ship - our hydraulic propeller system was constantly getting air bound and while we kept going over the system over and over again, we never could find the culprit. Then one day, we did - some sailor had (at some point) plugged a crack in a sampling line with a compound we refer to as 'monkey sht' kind of like industrial silly putty. Then, said sailor painted over the compound which made it impossible to tell without looking very close up. Pretty sad state of affairs....especially considering that sample line was coming off a 1000 PSI hydraulic system!

 

[flyer]

Im glad you caught that before it got ugly! Ive seen cracked mounts on 172' and 182's, but nothing like that.

 

[ajstoner21]

Wow! Thats a scary looking fracture.

Being an engineer, my advice would be to check the other mounts (and whatever the mounts are attached to), and make sure there isnt any other damage due to that mount breaking.

 

[Ted]

Wow! Thats a scary looking fracture.

Looks scarier than it is, since it was caught in time. Really scary would be the engine falling off.

Being an engineer, my advice would be to check the other mounts (and whatever the mounts are attached to), and make sure there isnt any other damage due to that mount breaking.

Being an engineer as well, I agree with your advice, and we've done that. We have found no additional damage. The plane is a good tank.

We will be keeping a close eye on the mount for the left engine, lest it suffer the same fate. No problems with it at the moment. I'm hoping to get this one back by the end of the week so the plane can be flying in time for Sunday.

 

[peter-h]

I would say one should check for obvious stuff like broken engine mounts at the 50hr check, when one changes the oil, cleans the plugs, etc.

It takes very little time to do a thorough inspection around the engine. One checks the exhaust system, the heater, basically everything visible.

But then I fly a single, and both cowlings need to come off to change the oil.

 

[Arbiter419]

Glad you found it sooner rather than later! Is that something you would've noticed during engine start/run up due to the vibration?

 

[jnmeade]

So, is 100 hours the right time, and if so, why? Many airplanes are inspected on condition or on a progressive maintenance period. Is 100 hours simply as good as any time frame, given that we don't have any particular reason for it other than some FAA dinosauer picked that number decades ago?
That engine mount could have cracked in the 10 hours after the annual or 100 hour. Would it have mattered? Maybe old airplanes should be inspected after every flight. _

 

[bbchien]

Yeowse!

 

[Ted]

Glad you found it sooner rather than later! Is that something you would've noticed during engine start/run up due to the vibration?

Well, I didn't notice it, and it didn't happen sitting in the hangar.

So my guess is probably not.

So, is 100 hours the right time, and if so, why? Many airplanes are inspected on condition or on a progressive maintenance period. Is 100 hours simply as good as any time frame, given that we don't have any particular reason for it other than some FAA dinosauer picked that number decades ago?
That engine mount could have cracked in the 10 hours after the annual or 100 hour. Would it have mattered? Maybe old airplanes should be inspected after every flight. _

Sure, you could have something like that break any time. It could break 1 hour after the 100-hour inspection. But the idea is a compromise between excess (every flight) and not often enough (every couple hundred hours).

In my experience, 100 hours is a good number. You find a few problems typically. They don't present a safety issue because you find them in time. However if you let them keep going, they would present a safety issue.

 

[gprellwitz]

So, is 100 hours the right time, and if so, why? Many airplanes are inspected on condition or on a progressive maintenance period. Is 100 hours simply as good as any time frame, given that we don't have any particular reason for it other than some FAA dinosauer picked that number decades ago?
That engine mount could have cracked in the 10 hours after the annual or 100 hour. Would it have mattered? Maybe old airplanes should be inspected after every flight. _

Listening to Jim Tweeto on Flying Wild Alaska, they do 75 hour inspections on all their planes. Of course, the consequences of a catastrophic failure in AK can be much more dangerous than in the lower 48!

 

[Ted]

Listening to Jim Tweeto on Flying Wild Alaska, they do 75 hour inspections on all their planes. Of course, the consequences of a catastrophic failure in AK can be much more dangerous than in the lower 48!

I don't know, I think "catastrophic" typically means "catastrophic." The ground doesn't hurt any less down here when you hit it.

 

[Ted]

They've got the new mount installed and have the whole plane pretty much back together.

The new mount looks very nice, and is definitely a significant improvement. Lots of gussets have been added that clearly will improve strength. The manufacturer (Kosola and Associates) has had this approved by the FAA with the engineering data to back it up.

I should do a short plug for Kosola and Associates now, as they really did a great job of getting the mount rebuilt. It wasn't the cheapest option, but the price varies depending on just how bad your mount is. I knew mine was bad, and they confirmed that yes, it really needed a lot of work. They did, however, get it done in a short amount of time in order to meet my desired schedule, understanding that the Aztec works for a living. That, combined with the fact that the mount is much better than it was even when leaving the factory back in 1969 makes me a happy customer. These people know their engine mounts, and are good to deal with.