Real Risk of Gear Box Failure

[MikeOH]

I've been religious about having the gears inspected at 100 and 200 hours per the AD/SB, but still hold my breath every time I put the gear down

Does anyone have data on how often the gears actually fail?  As in actual gear-ups due to gear failure.  How many failures actually prompted the AD?  I've heard tell that if you perform the proper periodic lubrications per the SB the gears will last indefinitely (well, not forever).  Any truth to that, or is a $10,000 replacement in my near future (5800 hours on the airframe and no entry showing replacement)?  My last inspection showed 'good to go' and, frankly, my mechanic seems non-plussed by the inspection (as in he's never seen an issue but I don't know how many he's actually done).

[N201MKTurbo]

It’s too bad you didn’t inspect them yourself. Then you would have a good idea of how fast they are wearing and how much life they have left.

I replaced my gears in 04 I think. My gear was horribly misrigged before that and chewed them up. Since then I inspect them every 200 hours and at this point, there is no detectable wear. So I think they will make it to the end.

[N201MKTurbo]

I have been working on Mooneys for 40 years. I have recently been working on other planes. One of the other planes are Cessna 310s. You look at our gear actuators. They are relatively small compact units. Then I work on a twin Cessna. The gear actuator is this monstrosity that is like 18 inches in diameter and six inches thick with a motor that looks like a Prestolite starter. 

You can probably buy those huge actuators by the pallet load at the junk yards for little money.

[Vance Harral]

Every few years, someone posts a question like this about the electric gear actuators and the related AD/SB.  Whether intended or not, I feel like it often has an air of, "The gears don't really wear out, right?  The AD is just a scam?"  But that's fine, nothing wrong with being skeptical and asking real owners what they've actually seen.  Every time the question is asked, though, I feel obligated to relay my anecdotal experience that yes, the gears really do wear out.

Specifically, in 2009, at ~2200 TT on our 1976 M20F, the 20:1 gears were worn to the point they failed the 1/2-tooth backlash test.  They had a scalloped shape, just like the SB/AD shows.  This happened despite dutifully servicing the actuator as required, during the 5 years we owned the airplane after purchasing it in 2004.  But we couldn't tell from the logs how often - if ever - the actuator was serviced prior to 2004.  It's possible the prior owners neglected to maintain them properly, and they wore out sooner than they otherwise would have.  But I'm also reasonably sure those 20:1 gears were original equipment from 1976.  Regardless of how they were maintained, I consider 33 years to be a pretty reasonable lifetime, and I was not upset about the replacement cost.

We installed 40:1 gears in 2009 (they were readily available then) and have serviced the actuator every other annual since.  In practice this works out to about 150 hour servicing intervals, which seems very reasonable.  The 100-hour "part 2" action in SB-190B is not possible with our particular actuator, as it has no grease fitting.  In fact, our actuator is actually an ITT LA11C2114 rather than the LA11C2110 called out in the SB.  So technically, neither the AD nor the SB applies to our particular aircraft.  But we act as if it did, per advice from Don Maxwell.

I have always performed the gear inspection myself, with a mechanic looking over my shoulder.  So I have lots of personal data points on what our gears look like over time.  Here in 2024, 15 years and another 1300 hours since the 2009 swap, I am definitely seeing a small amount of wear in our 40:1 gear set vs. what they looked like new.  The wear is almost undetectable from inspection to inspection, but cumulatively over time, even the 40:1 gears are developing a slight amount of scalloping.  I don't lose any sleep over this, and it's likely I'll be long retired from aviating before this set of gears fails the backlash measurement.  But I attest the wear is present, and something worth paying attention to - same as other long-term maintenance concern like exhaust, landing gear biscuits, engine overhaul, etc.

I freely concede that one data point from one owner isn't necessarily applicable to other airplanes.  But I disagree with the premise that properly-maintained gears last "indefinitely".  I've seen the wear over time with my own eyes.

[M20F]

Might tight armed turned 54 yesterday, still hasn’t let me down. 

[Ragsf15e]

34 minutes ago, Vance Harral said:

Every few years, someone posts a question like this about the electric gear actuators and the related AD/SB.  Whether intended or not, I feel like it often has an air of, "The gears don't really wear out, right?  The AD is just a scam?"  But that's fine, nothing wrong with being skeptical and asking real owners what they've actually seen.  Every time the question is asked, though, I feel obligated to relay my anecdotal experience that yes, the gears really do wear out.

Specifically, in 2009, at ~2200 TT on our 1976 M20F, the 20:1 gears were worn to the point they failed the 1/2-tooth backlash test.  They had a scalloped shape, just like the SB/AD shows.  This happened despite dutifully servicing the actuator as required, during the 5 years we owned the airplane after purchasing it in 2004.  But we couldn't tell from the logs how often - if ever - the actuator was serviced prior to 2004.  It's possible the prior owners neglected to maintain them properly, and they wore out sooner than they otherwise would have.  But I'm also reasonably sure those 20:1 gears were original equipment from 1976.  Regardless of how they were maintained, I consider 33 years to be a pretty reasonable lifetime, and I was not upset about the replacement cost.

We installed 40:1 gears in 2009 (they were readily available then) and have serviced the actuator every other annual since.  In practice this works out to about 150 hour servicing intervals, which seems very reasonable.  The 100-hour "part 2" action in SB-190B is not possible with our particular actuator, as it has no grease fitting.  In fact, our actuator is actually an ITT LA11C2114 rather than the LA11C2110 called out in the SB.  So technically, neither the AD nor the SB applies to our particular aircraft.  But we act as if it did, per advice from Don Maxwell.

I have always performed the gear inspection myself, with a mechanic looking over my shoulder.  So I have lots of personal data points on what our gears look like over time.  Here in 2024, 15 years and another 1300 hours since the 2009 swap, I am definitely seeing a small amount of wear in our 40:1 gear set vs. what they looked like new.  The wear is almost undetectable from inspection to inspection, but cumulatively over time, even the 40:1 gears are developing a slight amount of scalloping.  I don't lose any sleep over this, and it's likely I'll be long retired from aviating before this set of gears fails the backlash measurement.  But I attest the wear is present, and something worth paying attention to - same as other long-term maintenance concern like exhaust, landing gear biscuits, engine overhaul, etc.

I freely concede that one data point from one owner isn't necessarily applicable to other airplanes.  But I disagree with the premise that properly-maintained gears last "indefinitely".  I've seen the wear over time with my own eyes.

I had a set of 20/1 wear out too.  I think they were original but not certain.  If so they were 48 years old and ~5500 hours.  I was lucky as well and got a new set of 40/1s in 2015.

[jetdriven]

I’m really surprised that 20:1 gears were ever OK’d. The gear slams up and down and  shock loads on everything are so high it’s going to break and wear out stuff. 

[201Steve]

2 hours ago, jetdriven said:

I’m really surprised that 20:1 gears were ever OK’d. The gear slams up and down and  shock loads on everything are so high it’s going to break and wear out stuff. 

I think this is a good example of nobody expecting the airplane to be still flying 50 years later. 

[PT20J]

Are the 40:1 gears a Dukes part or something Mooney designed and manufactured for retrofit.

[Vance Harral]

The 40:1 gears were installed as OEM equipment in later-model Mooneys with additional lower doors on the landing gear, and higher Vle/Vlo speeds.  I presume they came from ITT, which was the manufacturer of the actuator at the time.  They are not a "retrofit" in the sense of being special, one-off parts, manufactured specifically to address SB 190B.  Rather, a case of using parts from a newer design in an older housing.

[Ragsf15e]

13 hours ago, PT20J said:

Are the 40:1 gears a Dukes part or something Mooney designed and manufactured for retrofit.

Good question.  Apparently mine came from lasar but that doesn’t say who manufactured them.  Here’s the writeup.  Apparently they were part of a Mooney kit?

[Matthew P]

If ANY of you have a set of old, non-serviceable gears, please send them my way, I am looking for a set for destructive testing so that I can determine the exact material composition in order to fabricate a set.

TIA

[skydvrboy]

Is it possible to upgrade these to the manual Johnson bar?  Seems like a much better and more robust design.

[Matthew P]

14 minutes ago, skydvrboy said:

Is it possible to upgrade these to the manual Johnson bar?  Seems like a much better and more robust design.

Evidently, my aircraft was delivered with the Johnson Bar and then "upgraded" to the Electrical Actuator, so I am assuming that it can be returned to the J-Bar, just finding the parts to do so..maybe someone on here has done that.

 

[Ragsf15e]

35 minutes ago, skydvrboy said:

Is it possible to upgrade these to the manual Johnson bar?  Seems like a much better and more robust design.

Someone has done it. It’s possible, but there are a couple that have collapsed due to not locking properly or having a worn out lock or ?? The electric gear is relatively bulletproof when properly maintained.  Pick your poison…

[A64Pilot]

It seems Cessna 210’s and Mooney’s gear up at similar rates. Don’t quote me, that’s a belief of mine. I know many 210’s have been geared up you can find it on inspection pretty easily.

Now I can’t prove it but have read it’s relatively uncommon for a 210 owner to forget to extend them, that the majority of gear ups are malfunctions.

Again I can’t prove it but I’ve read that Mooney gear failures are rare, and that the overwhelming majority of gears ups are from the pilot forgetting to put them down.

I used to worry about it, but have come to grips that the aircraft will be fixed, it’s an insurable event, in fact it’s THE reason I carry insurance.

Now I worry about eating a cam or a case cracking etc. , because you eat that cost.

 

[Fly Boomer]

31 minutes ago, A64Pilot said:

It seems Cessna 210’s and Mooney’s gear up at similar rates. Don’t quote me, that’s a belief of mine. I know many 210’s have been geared up you can find it on inspection pretty easily.

This was an informal "study" by Paul Bertorelli:

 

[201Steve]

Pretty wild statistic that mooney is twice the rate of a bo

[Fly Boomer]

7 minutes ago, 201Steve said:

Pretty wild statistic that mooney is twice the rate of a bo

What I did not get from Paul Bertorelli's video is whether those are percentages of all gear up landings, or percentages of gear-ups against registered aircraft by type, or percentages of attempted landings.  He probably isn't a mathematician.

[A64Pilot]

2 hours ago, 201Steve said:

Pretty wild statistic that mooney is twice the rate of a bo

Depends on how the stat is computed,  is it for instance percentage of all aircraft or is it biased by population size? For instance I think there are more Mooney’s than C-210’s, but perhaps as many 210’s are flown Commercially maybe their average usage is higher? If it were perhaps number per 1,000 hours flown it might be more representative?

Be interesting to know percentage of Mooney gear ups due to gear failure.

My personal take on it is my belief that there are many more low time Mooney drivers than other complex aircraft and that Mooney’s are often a pilots first complex over say the 210 or Bo crowd, and that maybe they forget more often than other type owners, or said another way maybe many Mooney gear ups are no fault of the airplane, where the 210 for instance usually is the airplanes fault.

You know when a 210 drops its gear, you see them and the drag increase is substantial. Personally I don’t drop my Mooney gear until the white arc and at that low speed there really isn’t much difference.

Long way of saying that as near as I can determine that actual gear failures in a Mooney exist of course, but are relatively rare.

Example, I have tried to find out how many actual no back spring failures have occurred on an Eaton actuator that resulted in a gear up without much success.

 

[hais]

On 5/19/2024 at 12:30 PM, MikeOH said:

I've been religious about having the gears inspected at 100 and 200 hours per the AD/SB, but still hold my breath every time I put the gear down

Does anyone have data on how often the gears actually fail?  As in actual gear-ups due to gear failure.  How many failures actually prompted the AD?  I've heard tell that if you perform the proper periodic lubrications per the SB the gears will last indefinitely (well, not forever).  Any truth to that, or is a $10,000 replacement in my near future (5800 hours on the airframe and no entry showing replacement)?  My last inspection showed 'good to go' and, frankly, my mechanic seems non-plussed by the inspection (as in he's never seen an issue but I don't know how many he's actually done).

Reading the title, I clicked quickly thinking you just got an STC for a Rotax

[warbingtonmasonry]

Good afternoon.

I have read here over the years several threads re: electric gear wear and ADs and malfunction worries.

Because of those worries, I have recently completed the removal of field-installed electric gear and installation of manual gear retraction system.

I have not yet checked the retraction system rigging. I don't really want to spend $350 for two rigging tools.

The tools appear to me to provide a secure way to fasten a torque wrench to the retraction truss at a certain point in space for which the overcenter break torque is specified.

My 1967 M20F left the factory with manual gear retraction system.

I plan to offer my complete electric retraction system, as removed, for sale soon.

[N201MKTurbo]

11 minutes ago, warbingtonmasonry said:

Good afternoon.

I have read here over the years several threads re: electric gear wear and ADs and malfunction worries.

Because of those worries, I have recently completed the removal of field-installed electric gear and installation of manual gear retraction system.

I have not yet checked the retraction system rigging. I don't really want to spend $350 for two rigging tools.

The tools appear to me to provide a secure way to fasten a torque wrench to the retraction truss at a certain point in space for which the overcenter break torque is specified.

My 1967 M20F left the factory with manual gear retraction system.

I plan to offer my complete electric retraction system, as removed, for sale soon.

I would check your preloads before you fly it. When they put in the electric actuator, did they change the nose gear retraction rods to the ones with the springs? If not, getting the nose gear preload correct takes a bit of work.

[Andy95W]

The gear rigging tools really are that important, please at least borrow or rent them to set the pre-loads initially.  Many shops do have them (some may not know what they’re for.)

Too tight and you risk bending a tube or breaking a nose gear truss at a weld.  Too loose and you risk the overcenters not holding the gear down.  Either way, you get a gear collapse.

[PT20J]

Without the rigging tools, how do you check the preload which is supposed to be checked as part of the annual inspection?