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Are all three gear really down?


Mooneymite

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There have been numerous threads on MS about making sure the gear is down for landing, but all these discussions are about the pilot putting the gear handle in the correct position.  Personally, I think Mooney's gear down verification system stinks and we are all subject to gear up landings due to a[poorly designed gear indicating system.

It is completely possible due to Mooney's design that the handle (or Johnson bar) could be in the down position and one or more gear not down and the pilot would never know it....until too late.

If you look at the attached picture, there are two switches on the left gear pushrod....one for up, one for down.  However, there is no indication of the status of the individual over-center mechanisms for each individual gear.

In theory, one could disconnect all the push-rods to the gear and get perfect down and locked indications while all gear are 'not down'.

In reality, a push-rod could be bent, the over-center lock not over-center and the pilot would never know until too late....unless he just happened to find it during a fortuitously timed inspection.

I wonder why Mooney did not design individual gear down-lock status lights like most other aircraft?  Why did Mooney feel "one green" would suffice for the traditional "three green"?

 

20170420_111734.jpg

Bent Push-rod.jpg

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Not to discount the finding out by surprise, but since there is no backup gear retraction mechanism, what will do you about it if it happens?

I can only theorize they thought similarly and chose not to add additional components that could fail that didn't add much value.

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1 minute ago, smwash02 said:

Not to discount the finding out by surprise, but since there is no backup gear retraction mechanism, what will do you about it if it happens?

I can only theorize they thought similarly and chose not to add additional components that could fail that didn't add much value.

Back up gear retraction???   Huh?

This is about making sure all three gear are actually down.....not up.  Should a gear rod become disconnected, or bent, the hapless Mooney pilot would have no clue.  On other aircraft, if a pilot fails to get three green lights, there are things like slipping the plane, or preparing for a collapse upon landing that can be done.  For us Mooney drivers, it's a complete surprise.  I think a microswitch on each over-center brace would be of great value compared to the "lying linkage" system we have.

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There are a lot of systems that have no back-up...

When operating properly, one wheel down and locked means the other two are down, and locked too.

I have two indicators.  One physical on the floor, and one, a light on the panel...

17 years of Mooney flying, no bent landing gear parts yet...  :)

If we are to come up with a system that identifies bent tubes, let's check them all...?

Starting with the nose gear steering parts... (bad towing operator)

Poorly maintained over center limits...  (crummy maintenance personnel)

If a tube bends during flight, and if I were to know about it... How would I handle that?  A light that tells me to land gear up on a hard surface?

Best regards,

-a-

Edited by carusoam
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I had this problem in my previous Mooney.  My right main gear did not extend and I had no idea because the gear down light came on when the Johnson bar locked into the block.  Fortunately there was someone holding short who noticed my problem when I was on short final. They jumped on the radio to tell me and I was able to go around.  In the end I decided it was safest to retract the other two and land on the belly.

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I guess my question is to what extent Mooneys have suffered more, or more injurious/fatal accidents as a result of this "flaw" in the indicator system, vs. GA retractables with per-wheel indicators?  We have 50+ years of data on this, what does it say?

You're certainly correct that there are failure modes which are not caught by the current indicator system.  But it's not clear a different system would save more lives or dollars.  Don't forget that a more complex indicating system would have more complex indicator failures, potentially leading to bad outcomes that would not have happened with the simpler system.  In my 25+ year career in engineering, I can't tell you how many times I've seen systems that were (re)designed to catch some corner-case failure, actually wind up causing more trouble than the original corner case.

My gut instinct is that when each wheel is an independent system (e.g. hydraulic), independent indicators are a good solution.  With the mechanical linkages in our Mooneys, the combination of an electric (switches) and mechanical (floor line) indicator seem quite adequate.

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I agree with Vance. Unless data shows an abnormally high instance of gear failure problems with the Mooney, which I don't think it does, the current indication system is more than adequate. The simpler, the better. 

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4 minutes ago, aviatoreb said:

Is it possible for the mechanical indicator window on the floor to show down (the green box) if the gear is not fully down?

Yes, but only if there's been a major mechanical malfunction, such as the bent pushrod discussed above.  The whole system consists of a series of interconnected pushrods.  The switches and lights track the position of one of those pushrods, while the floor indicator tracks another.  You can see exactly which pushrods are monitored by looking in your parts manual and/or at your airplane next time you have the belly panels off.  But nothing tracks the "final" pushrods attached to the gear trusses and/or the over-center links, hence Mooneymite's concern

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7 minutes ago, Vance Harral said:

 I can't tell you how many times I've seen systems that were (re)designed to catch some corner-case failure, actually wind up causing more trouble than the original corner case.

Amen,

We did an FMEA on a piece of medical equipment and put checks in for every item on the list. It would shut down for every fault. 

It was so unreliable that it was almost unusable. I finally convinced them to let me just log the errors and it ran forever.

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I suspect that the reason we only have one indicator is that all three gear are mechanically connected.  Barring a hardware failure, if one is down, all of them are down.  With most other airplanes, the gear is hydraulically actuated so there is a much greater chance of an individual gear failing.  With a hydraulic system you can have a pressure failure, one of (at least) three actuators failing, electrical sequencing failure, or an indicator failure.  With ours, except in an extremely rare case, either they are all up or all down.  Watch the gear come up or down on a Cessna, Piper, or Rockwell.  The gear comes up in fits and pieces.

I'm happy with our system.

Don't forget about the United DC8 that ran out of fuel over Portland because they thought they had a gear failure when all they really had was a light bulb failure.

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2 hours ago, aviatoreb said:

Is it possible for the mechanical indicator window on the floor to show down (the green box) if the gear is not fully down?  Question - not a statement.

Kind of.  It is a pretty simple sliding mechanism connected directly to gear.  But if the plexiglass breaks by say someone stepping on it, it can misrepresent the status.

 

The gear system is so well designed it really is down or up and if all three are not down...   Does not matter...

20160810_013738.jpg

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Kind of.  It is a pretty simple sliding mechanism connected directly to gear.  But if the plexiglass breaks by say someone stepping on it, it can misrepresent the status.
 
The gear system is so well designed it really is down or up and if all three are not down...   Does not matter...
20160810_013738.thumb.jpg.66cc1ec9b31cf2d20c47a03cc293ae40.jpg


I had this piece break on mine back in the 1990s. I retracted the gear and it still showed gear down. I concluded it was up because I was able to reach cruise speeds with normal power settings.

My next concern, not knowing the system, was that maybe it would not come down. I elected to fly the 300 nm back home this way and made the decision if it didn't come down, I would be able to have the resulting gear up at my home airport. It came down and I later,learned how that piece just slides back and forth.


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3 hours ago, carusoam said:

 

There are a lot of systems that have no back-up...

This is not a system....it is an indicator for the gear system.  Its purpose is to tell us if the gear are down, not that a single push-rod is "in place".  There are backups for the gear system....at least on my Mooney.

When operating properly, one wheel down and locked means the other two are down, and locked too.

And that's the point:  Only "if" operating properly.  If operating properly, we only have to look at the gear handle, we don't need the light, or stripe at all.

I have two indicators.  One physical on the floor, and one, a light on the panel...

Both indicators show basically the same thing.  Neither can actually verify the position of the gear.

17 years of Mooney flying, no bent landing gear parts yet...  :)

..."Yet", that's an important word.  19 years for me and I'm glad I caught it, even though it was "just luck".

If we are to come up with a system that identifies bent tubes, let's check them all...?

Huh?  I just want to know if each gear is down and locked.  :wacko:  The more you look at the Mooney gear system, the more you see that there are multiple ways for the gear to fail and not know about it.  Happily it is a pretty simple system.  I would like to know how many gear collapses were caused by undiscovered bent push rods.

 

 

-a-

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1 minute ago, Mooneymite said:

I would like to know how many gear collapses were caused by undiscovered bent push rods.

If you're serious, this seems pretty straightforward.  Search NTSB records for Mooney gear-up landings, subtract out the ones where a per-wheel indicator wouldn't help you (e.g. collapsed after rollout, forgot to put the switch down, etc.).  Everything left *might* be a failure of the type you describe.  My guess is that number is very tiny, but I haven't researched it myself.

Based on having inspected and handled the pushrods in question, it seems like it would take a tremendous amount of force to bend one in the manner seen in your photo above.  How did that happen?  It seems almost inconceivable to me that an electric gear actuator could do that (circuit breaker would pop first).  If that's from a manual-gear airplane, it would seem someone with major muscles (or major motivation) must have really leaned into it.

All that said, if this is really a concern for you, may I suggest installing a live streaming camera - e.g. a Garmin VIRB.  The FAA has essentially capitulated on such things being "portable" devices that require no special approval to install.  Clamp one on your tail tie-down such that it can see all three wheels.  When you put the gear down, just take a look at the live streaming picture on your tablet or phone to confirm.

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1 hour ago, Yetti said:

Kind of.  It is a pretty simple sliding mechanism connected directly to gear.  But if the plexiglass breaks by say someone stepping on it, it can misrepresent the status.

 

The gear system is so well designed it really is down or up and if all three are not down...   Does not matter...

20160810_013738.jpg

I just adjusted that last night. Now my lines line up perfectly when the gear is down!

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I would suspect most gear failures caused by bent rods are not naturally occurring. I suspect they are caused by someone trying to fix a perceived problem with the gear system. Most likely trying to adjust the preload.

When the gear system is assembled and adjusted properly it would be almost impossible to bend a rod without crashing. 

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4 hours ago, Mooneymite said:

There have been numerous threads on MS about making sure the gear is down for landing, but all these discussions are about the pilot putting the gear handle in the correct position.  Personally, I think Mooney's gear down verification system stinks and we are all subject to gear up landings due to a[poorly designed gear indicating system.

It is completely possible due to Mooney's design that the handle (or Johnson bar) could be in the down position and one or more gear not down and the pilot would never know it....until too late.

If you look at the attached picture, there are two switches on the left gear pushrod....one for up, one for down.  However, there is no indication of the status of the individual over-center mechanisms for each individual gear.

In theory, one could disconnect all the push-rods to the gear and get perfect down and locked indications while all gear are 'not down'.

In reality, a push-rod could be bent, the over-center lock not over-center and the pilot would never know until too late....unless he just happened to find it during a fortuitously timed inspection.

I wonder why Mooney did not design individual gear down-lock status lights like most other aircraft?  Why did Mooney feel "one green" would suffice for the traditional "three green"?

 

20170420_111734.jpg

Bent Push-rod.jpg

You should paint your rods all grey or all black. I couldn't fly a plane with different color rods!

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Our gear system is a 4 bar linkage. It is impossible, without mechanical failure of a pushrod, to get two gear down and leave one partially down. With the strength of the tubing used, normal operation will not bend one. Four bar linkages either all move, or all don't move.

What happened to yours, Gus? I'm genuinely curious, we have the same plane. I'll fly up and buy you a beer for the whole story!

Edited by Hank
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50 minutes ago, Vance Harral said:

If you're serious, this seems pretty straightforward.  Search NTSB records for Mooney gear-up landings, subtract out the ones where a per-wheel indicator wouldn't help you (e.g. collapsed after rollout, forgot to put the switch down, etc.).  Everything left *might* be a failure of the type you describe.  My guess is that number is very tiny, but I haven't researched it myself.

Or....find out how many replacement gear push-rods are ordered?

If the gear system is as reliable as we think, why would gear push rods ever need to be replaced?

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There are a lot of systems that have no back-up...
This is not a system....it is an indicator for the gear system.  Its purpose is to tell us if the gear are down, not that a single push-rod is "in place".  There are backups for the gear system....at least on my Mooney.
When operating properly, one wheel down and locked means the other two are down, and locked too.
And that's the point:  Only "if" operating properly.  If operating properly, we only have to look at the gear handle, we don't need the light, or stripe at all.
I have two indicators.  One physical on the floor, and one, a light on the panel...
Both indicators show basically the same thing.  Neither can actually verify the position of the gear.
17 years of Mooney flying, no bent landing gear parts yet...  
..."Yet", that's an important word.  19 years for me and I'm glad I caught it, even though it was "just luck".
If we are to come up with a system that identifies bent tubes, let's check them all...?
Huh?  I just want to know if each gear is down and locked.  :wacko:  The more you look at the Mooney gear system, the more you see that there are multiple ways for the gear to fail and not know about it.  Happily it is a pretty simple system.  I would like to know how many gear collapses were caused by undiscovered bent push rods.
 
 
-a-


With today's technology, ever think about mounting a small vehicle backup camera on the belly and using your iPad, iPhone or cell phone to display it? I see Costco even sells with a display.


Sent from my iPhone using Tapatalk Pro
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52 minutes ago, Vance Harral said:

All that said, if this is really a concern for you, may I suggest installing a live streaming camera - e.g. a Garmin VIRB.  The FAA has essentially capitulated on such things being "portable" devices that require no special approval to install.  Clamp one on your tail tie-down such that it can see all three wheels.  When you put the gear down, just take a look at the live streaming picture on your tablet or phone to confirm.

That would be about as effective as the present green light/stripe.  As you are aware, the gear can appear down, but if the over-center brace is not over-center, the gear is being held down by the push rod.....

A micro switch on the over-center brace like other aircraft manufacturers use would be best.

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