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Throttle Became Disconnected from the Throttle Arm


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1968 M20F

The other day, I was reminded once again that when it comes to aviation, you always need to be ready for anything. 

My throttle cable became disconnected at the throttle arm.

My wife and I had landed a few days prior at KAAF (a great place for raw oysters and seafood!). It had been a great IMC/IFR flight, and we flew almost down to the circling minimums before we broke out and circled, landed, taxied in, and shutdown. 

A few days later, we were to depart. But allow me to back up - like many of you, I suspect, I normally set about 1100 RPM just before I pull the mixture when shutting down. And generally use the Don Maxwell "How to start a Lycoming fuel injected engine" methodology for starting. And that's exactly what I had done. The approach and landing was fine. Taxing was fine. Setting 1100 RPM was fine. Normal shutdown.

But two days later, as soon as I cranked up, I knew we had a problem.

The throttle was completely unresponsive.

I shut her down and asked Jim, Centric Aviation's mechanic to take a look. After removing the cowlings, he found that the linkage was disconnected at the throttle arm. Still on the arm, held by a thin layer of engine oil/residue, was the washer. The bolt was found nearby in the lower cowling. 

But both the cotter pin and the castellated nut were missing. Gone. Vanished.

Jim got us fixed up and going in no time at all.  By the way, all the people at Centric Aviation/KAAF are great, great folks.  They treat us like royalty every time we go there.  

I'm so thankful/lucky/blessed that it didn't happen when we were airborne, and in the clouds. At WOT. 

Or worse yet, near idle, in the clouds, while slowing down to configure.

Our planes back home now, at KFFC, and in its annual, and I'm having them look closely at that particular linkage for any signs of anything in the proximity that could cause a cotter pin to fall out.  Of course, I've asked them to look closely at all my other linkages for condition and security.

So now this is to you, gentle reader. What else can we, this awesome community of Mooney enthusiasts, learn from this incident? 

I'm all ears.

 

 

Edited by redcatcher27
The title wasn't clear enough
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Congratulations on having good fortune on your side.   In flight with a stuck open throttle creates interesting challenges to test a the pilot's dead-stick landing skills.

The last annual presented a great opportunity for someone to observe the missing cotter pin, if it was missing then.  The importance of putting eyes and/or fingers on every critical linkage with some regular frequency can't be overstated. 

The timing seems odd given that at last shutdown that bolt must have been in place.   The drag on the throttle plate must have created some shear on the bolt that disappeared when you shut the engine off, and allowed the bolt to come on out.  The nut and pin probably blew out the cowl flap opening.

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A second set of eyes during maintenance on flight or power plant controls is one way to help avoid this.  In Canada it’s require by regulation.

Also switching to MS17825 self locking castle nuts which have a nylon insert give a second chance should the cotter pin fall out or be missed, installing a stainless steel cotter pin which is much stronger.

Clarence

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19 minutes ago, M20Doc said:

A second set of eyes during maintenance on flight or power plant controls is one way to help avoid this.  In Canada it’s require by regulation.

Also switching to MS17825 self locking castle nuts which have a nylon insert give a second chance should the cotter pin fall out or be missed, installing a stainless steel cotter pin which is much stronger.

Clarence

Thanks so much for your response, Clarence.

Funny, but that is precisely what was reported to me this morning from the repair facility doing my annual - they said they had replaced the castellated nut with one that incorporated a nylon insert, along with a stainless steel cotter pin (at no charge!)  - they didn't give me part numbers, but I'm confident its the one you indicated. 

As you said, with the nyloc nut, along with a stainless steel cotter pin, you essentially end up with a double safety there.

Given what happened to me - I would highly recommend that EVERYONE have this done at their next annual.

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  • redcatcher27 changed the title to Throttle Became Disconnected from the Throttle Arm

If a cotter pin falls out, it’s almost certainly one that has been reused, and bending it back and forth of course causes a fatigue crack, so later it breaks and falls out.

A cotter pin should really never be under much of any shear forces, it’s like safety wire, it prevents the beginning of movement so strength isn’t really called for, but saying that stainless steel isn’t as strong as carbon steel, if it were then surely crankshafts and connecting rods would be stainless. Although stainless is a generic term like plastic and encompasses many materials the majority of aircraft corrosion resistant fasteners are either 304 or 316, 304 is also called 18/8, monel is sometimes also mistakenly called stainless, it’s much more expensive though.

https://monroeengineering.com/blog/whats-the-difference-stainless-steel-vs-carbon-steel/

US Military also requires everything to be inspected, coming into the FAA world that took me a long time to get over as in the Army anyway, you could not inspect your own work.

On edit, strength is also another word that can mean many different things, SS is usually very ductile and ductility is very much desired in things like cotter pins, so it’s a very good cotter pin material, assuming of course it’s soft SS.

Edited by A64Pilot
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In an ideal world you can inspect your own work...

In the human world, with human frailties...

Even our pre-purchase inspections are done by Mooney specific mechanics that are independent of the owner and last maintainer...

Because as the new owner... failure is not an option... :)

Its fun being a human being...

Best regards,

-a-

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1 minute ago, carusoam said:

In an ideal world you can inspect your own work...

In the human world, with human frailties...

Even our pre-purchase inspections are done by Mooney specific mechanics that are independent of the owner and last maintainer...

Because as the new owner... failure is not an option... :)

Its fun being a human being...

Best regards,

-a-

Years ago Boeing tried the self inspection thing, I forgot the name, but it was a miserable failure. Two sets of eyes are better than one, Army went to two pilots in every aircraft based in that, the likely hood of both pilots making a mistake is much less than one.

On edit, I think the Boeing program may have been called total quality management or something similar?

Edited by A64Pilot
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I had this happen on my O320 on my Super Cub. It came out in flight and the throttle ranged between 2300 and 2200. I was enroute to my home base, so I was able to text my mechanic and tell him I may need a tow from the runway to the hangar. I came overhead, and modulated the engine with the mixture until I had the field made, then went to cut off and dead stick landed it. Of sheer luck and not skill, I rolled out right up to my mechanics truck, where he had the. requisite bolt, pin and nut waiting!

 

 

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I’m trying to think of the airplane, but one I’ve seen had a spring that if the throttle cable broke or came loose, the engine would go to full throttle as opposed to idle.

‘I’m not saying do this as it’s not legal, just thought it a good idea.

Edited by A64Pilot
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couple of years ago asked the MSC to install a new throttle cable.  I take it for its first flight and the throttle disconnects upon touchdown.  Engine revs to 2000 plus RPM.  Had to use the mixture control to taxi back over a mile to the shop....turns out that the shop had it all dorked up and it was dorked up for two plus years until Phil in Avon Park FL fixed it this year with mooney parts that the MSC never thought to consider.  

note....not all MSC are created equal.....

 

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On 4/24/2021 at 4:59 PM, A64Pilot said:

If a cotter pin falls out, it’s almost certainly one that has been reused, and bending it back and forth of course causes a fatigue crack, so later it breaks and falls out.

A cotter pin should really never be under much of any shear forces, it’s like safety wire, it prevents the beginning of movement so strength isn’t really called for, but saying that stainless steel isn’t as strong as carbon steel, if it were then surely crankshafts and connecting rods would be stainless. Although stainless is a generic term like plastic and encompasses many materials the majority of aircraft corrosion resistant fasteners are either 304 or 316, 304 is also called 18/8, monel is sometimes also mistakenly called stainless, it’s much more expensive though.

https://monroeengineering.com/blog/whats-the-difference-stainless-steel-vs-carbon-steel/

US Military also requires everything to be inspected, coming into the FAA world that took me a long time to get over as in the Army anyway, you could not inspect your own work.

On edit, strength is also another word that can mean many different things, SS is usually very ductile and ductility is very much desired in things like cotter pins, so it’s a very good cotter pin material, assuming of course it’s soft SS.

I’ve seen many new MS24665 carbon steel cotter pins break just as they were being installed in the castle nut.  I’ve never experienced the same with a stainless steel version.

Clarence

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On 4/26/2021 at 4:51 PM, 1964-M20E said:

Ok glad you had the incident on the ground not in the air.

 

Now the more important question what restaurants are close by that are good?

 

 

So, there are many great restaurants and local dives to choose from in Apalachicola. I keep a car parked there at KAAF, so I'm not 100% certain, but I believe the FBO there has a courtesy car. and Apalachicola is only about 4 miles away.  The Owl Cafe is perhaps my favorite for a full dinner, but below that is "The Tap Room" and it has more of a bar room ambience. Both place's serve "Duck Fries", which are pulled duck confit fries with crispy prosciutto and duck cracklins. So good! 

The one place I think you probably must see is "Hole In the Wall". Go at an off time, when its not so crowded, or you'll never get a seat - the place is TINY. Sit at the bar and have some raw oysters. You won't be disappointed by the show put on by the three main characters/owners/operators there - Dwayne, Barbara, and Danny. Its their crazy, country, and continuous banter back and forth between them and their patrons that will leave you in stitches. Something between Seinfeld's soup nazi and a slap stick sideshow.  

Many other places in between, but they all serve great seafood. If you need a place to stay, and you're not a CB (I know, wrong website, right?) there's the historic Gibson Hotel.

For a quick breakfast the next morning before you get back in the air, Cafe Con Leche.

Enjoy!

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4 hours ago, Yetti said:

I just can't see a properly done cotter pin coming out.   Especially in that low stress area. When was the last time that area of the plane was worked on?

Well, at the previous oil change I'm sure it was visible. Before that, at its annual, about 11 months prior.

And I know where you're going with this - it should not have happened it everyone was being attentive to details.

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2 hours ago, redcatcher27 said:

So, there are many great restaurants and local dives to choose from in Apalachicola. I keep a car parked there at KAAF, so I'm not 100% certain, but I believe the FBO there has a courtesy car. and Apalachicola is only about 4 miles away.  The Owl Cafe is perhaps my favorite for a full dinner, but below that is "The Tap Room" and it has more of a bar room ambience. Both place's serve "Duck Fries", which are pulled duck confit fries with crispy prosciutto and duck cracklins. So good! 

The one place I think you probably must see is "Hole In the Wall". Go at an off time, when its not so crowded, or you'll never get a seat - the place is TINY. Sit at the bar and have some raw oysters. You won't be disappointed by the show put on by the three main characters/owners/operators there - Dwayne, Barbara, and Danny. Its their crazy, country, and continuous banter back and forth between them and their patrons that will leave you in stitches. Something between Seinfeld's soup nazi and a slap stick sideshow.  

Many other places in between, but they all serve great seafood. If you need a place to stay, and you're not a CB (I know, wrong website, right?) there's the historic Gibson Hotel.

For a quick breakfast the next morning before you get back in the air, Cafe Con Leche.

Enjoy!

cool sounds like a road trip.

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3 hours ago, redcatcher27 said:

Well, at the previous oil change I'm sure it was visible. Before that, at its annual, about 11 months prior.

And I know where you're going with this - it should not have happened it everyone was being attentive to details.

Not really. It's not that visible.  You have to take the starter and alternator off to change out the fuel servo. I am going with the last person that had the throttle cable connected up probably forgot to put a cotter pin in or forgot to do it properly.   There is a sequence of washers to prevent binding and such.    While I will check mine, I am more sure that it was done properly because I was the one that did it.   First two pics are before taking it off.   Note on the throttle arm that you are putting the cotter pin in blindly.   so you would have to get a mirror or cell phone camera to inspect.

IMG_20190222_133739.jpg

IMG_20190222_103240.jpg

IMG_20190331_102323.jpg

IMG_20190419_194200.jpg

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On 4/27/2021 at 8:12 AM, GeeBee said:

I had this happen on my O320 on my Super Cub. It came out in flight and the throttle ranged between 2300 and 2200. I was enroute to my home base, so I was able to text my mechanic and tell him I may need a tow from the runway to the hangar. I came overhead, and modulated the engine with the mixture until I had the field made, then went to cut off and dead stick landed it. Of sheer luck and not skill, I rolled out right up to my mechanics truck, where he had the. requisite bolt, pin and nut waiting!

 

 

In the late 90s, I had just completed my IFR check ride at KORF in my 64E.  On climb out from Norfolk on my return to KCPK, my throttle became unresponsive.  I also chose to use the mixture and continue my return to my home field, about 15nm from ORF.  When I returned to my hangar, found the throttle bracket was not only disconnected but gone!

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3 hours ago, Yetti said:

Not really. It's not that visible.  You have to take the starter and alternator off to change out the fuel servo. I am going with the last person that had the throttle cable connected up probably forgot to put a cotter pin in or forgot to do it properly.   There is a sequence of washers to prevent binding and such.    While I will check mine, I am more sure that it was done properly because I was the one that did it.   First two pics are before taking it off.   Note on the throttle arm that you are putting the cotter pin in blindly.   so you would have to get a mirror or cell phone camera to inspect.

IMG_20190222_133739.jpg

IMG_20190222_103240.jpg

IMG_20190331_102323.jpg

IMG_20190419_194200.jpg

I don’t think that there is a requirement for the installation direction of the bolt and nut.  Why not flip it around with the nut aimed outward making cotter pin installation and future inspection easier?

Clarence

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7 hours ago, M20Doc said:

I don’t think that there is a requirement for the installation direction of the bolt and nut.  Why not flip it around with the nut aimed outward making cotter pin installation and future inspection easier?

Clarence

Mechanically I think your proposal is sound, there is just voice saying that you install the nut away from heim joint.    And I guess I was assuming that the OP did not have the old style connector.   My buddy found one on the plane he just did.   yes replace it.   But this could explain the cable coming unconnected.    There is a Mooney SB. 

 

 

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Not Mooney related, but disconnected throttle related.

This family of four had their throttle disconnected mid-flight and engine automatically going into full power. They were able to land manipulating mixture. The video and explanation is pretty good.

https://www.youtube.com/watch?v=q-Y99df66rY

 

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The Commercial Cert. is underrated. Sure, there are alot of maneuvers that you will probably never fly again in your career unless you find yourself in a Sopwith Camel needing to turn and gain altitude before attacking a pursuing Fokker (that’s the chandelle). But the power off landing skills are invaluable, especially for single engine pilots.

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