tail tiedown weight

[Bob_Belville]

I just wonder what other maint procedures people disregard the instructions on because they don't agree with it or Mooney hasn't told them why it's done this way!

ISTM, "disregard" is much too strong a word. The A&P usually has considerable latitude when it comes to methods and determination of airworthiness. "Recommended" or "not recommended" is not mandatory. Intentionally. I suppose. Frankly, I would rather have my plane (and my neck) in the hands of a smart, experienced A&P who thinks than a legalist who follows the letter of the law by rote.

[jetdriven]

I just wonder what other maint procedures people disregard the instructions on because they don't agree with it or Mooney hasn't told them why it's done this way!

For example, the SMM instructions on how to repair the cowl, #181 9oz fiberglass cloth and obsolete paste style patching epoxy compound. No mention of newer styles of glass, carbon fiber, vacuum bagging, or high temp MGL epoxy.  Its just obsolete, but they could update the info.

[Sabremech]

As a professional A&P who's in aviation for a living you have to look at all the data and it's my licenses that are on the line so I can be all the legalese I want to be. Yes there is leeway in the decisions we can make, but do you honestly believe that what's called out in this service information letter is all that difficult to follow? Is it that much more work to jack the airplane a different way? Why the resistance to changing how things are done? This is a simple change and not that difficult to do, so to purposely choose not to follow it is disregarding maint instructions. It's quite obvious that Mooney has some concerns with how the airplanes have been jacked for the last 40 years. Do you think maybe they found a better way and want to ensure we don't create a problem during the next 40+ years of life?

You should look for an A&P that can both use common sense but who also covers your butt when it comes to the legal aspects of your maint.

We can turn this into the push your airplane by the prop debate, but I'll choose to leave it at this. If I worked on your airplane, I would jack it by the updated (recommended) maint instructions. I'd rather have an owner ask me why I'm doing it that way than another owner jumping down my throat for not jacking it to the new data.

Thanks,

David

[Bob_Belville]

As a professional A&P who's in aviation for a living you have to look at all the data and it's my licenses that are on the line so I can be all the legalese I want to be. Yes there is leeway in the decisions we can make, but do you honestly believe that what's called out in this service information letter is all that difficult to follow? Is it that much more work to jack the airplane a different way? Why the resistance to changing how things are done? This is a simple change and not that difficult to do, so to purposely choose not to follow it is disregarding maint instructions. It's quite obvious that Mooney has some concerns with how the airplanes have been jacked for the last 40 years. Do you think maybe they found a better way and want to ensure we don't create a problem during the next 40+ years of life?

You should look for an A&P that can both use common sense but who also covers your butt when it comes to the legal aspects of your maint.

We can turn this into the push your airplane by the prop debate, but I'll choose to leave it at this. If I worked on your airplane, I would jack it by the updated (recommended) maint instructions. I'd rather have an owner ask me why I'm doing it that way than another owner jumping down my throat for not jacking it to the new data.

Thanks,

David

David, beyond the CYA rhetoric, do you concede using the "tail hook" is not prohibited by the SI? Several MSCs and other very experienced and respected shops apparently continue to use the tail tie down. Are you calling them irresponsible? 

 

As others have pointed out, there are older planes with the squirrel cage inner cowl (whatever it's called) whose engine lift hook is removed. Someone told us it was 2 hours to get the cowl and baffle off. I suppose another 2 hours to put it back. At say $75/hr shop rate that adds $300 to the bill if he wants to raise the gear to remove the plastic housing behind the JBar as I will be doing this week.

 

The jack points on my E are well ahead of the gear. So when the plane is on jacks it probably only takes ~50 pound of weight at the long arm at the tail hook to hold the nose off. I am going to verify the estimate this week.

[Marauder]

What I read in the SB was Warning, Caution, Caution, Note -- with the note being the tail weight comment. They use the word "recommend" not the "DO NOT" associated with the warning. I suspect they saw something that happened in an isolated situation and are recommending not to do it. Has anyone taken the time to get off their soap box and call Mooney directly for clarification?

[Sabremech]

What's the justification or reason not to follow the instructions in Mooney SI M20-114? Any top MSC care to share why they do or don't follow the instructions in this service letter?

[Bob_Belville]

David, I did not, and would not have, named any MSCs specifically. I would not expect them to speak up on this very public list. But I think several of us have given adequate justification: it is legal, it is safe (in the experience and expert opinion of the shop/A&P) and it saves time and money. 

[fantom]

What's the justification or reason not to follow the instructions in Mooney SI M20-114? Any top MSC care to share why the do or don't follow the instructions in this service letter?

 

Could be....umm....common sense  Different strokes!

[Sabremech]

It's been stated that the Mooney is no different than any other low wing airplane and that jacking from the tail is ok on the other brands and therefore ok on the Mooney. The construction of the cabin section of the Mooney is not like that of the other low wing brands. How many places is the aluminum that makes up the cabin shell on the Mooney secured to the 4130 steel cage? Is it as strong as the cabin or tail for that matter of say a Piper Cherokee or Beechcraft Bonanza?

[JaredDavis]

I have a 65 C with a dog house. When we are jacking it for an annual there is no time difference to follow the SI. We pull off the top of the doghouse to inspect the engine anyway. The lift point is adjusted from the stowed position in about 30 seconds.

 

On my plane, it takes much less than 1hr to remove the top cowl and the top of the doghouse.

[jetdriven]

It's been stated that the Mooney is no different than any other low wing airplane and that jacking from the tail is ok on the other brands and therefore ok on the Mooney. The construction of the cabin section of the Mooney is not like that of the other low wing brands. How many places is the aluminum that makes up the cabin shell on the Mooney secured to the 4130 steel cage? Is it as strong as the cabin or tail for that matter of say a Piper Cherokee or Beechcraft Bonanza?

If my tail was going to fall off with 100 lbs of downforce on the tail tiedown ring, I'd rather it do so in the shop, on jacks, than in flight

[Sabremech]

In a real effort to get to the 'why' the new procedure, I presented some questions hoping to get some good thoughtful answers. I thought I would at least get that from Byron and a few others, but sarcasm seems to be the only answers I see. I put a call into Mooney today and left a voicemail. Maybe I'll get an answer, maybe not, but at least I'm trying to find out the why so we can put this to rest.

By the way Byron, it takes more than 100 pounds to hold the tail down on my C model. I don't think this is an issue where the tail will fall off, but I think I'm on the right track with the questions in my last post.

We'll see.

[jetdriven]

In all seriousness, David, I read the service letter and it seems like lawyers wrote it for Mooney. Established procedure for the past many years seems to work well, is quick, and is troubl free so long as you dont have one person leaning on the engine while working on it while someone else hops on the front of the wing to lean over and help the engine worker, it did flop up and back down, but nothing was harmed

 

FWIW we did try the SB method of jacking, and we are putting a lot of stress on the engine lifting eye and the engine mounts. they are not designed to absorb vertical loads like when lifting the front of an airplane with it. It really stretched out the rubber mounts.  Also, we managed to bang the prop on the arm of the engine lift, which isnt good for it.  Plus the airplane can now fall off the jacks easier, because the engine lift does not positively locate the nose of the airplane. The hoist is on wheels, and it can move now, and someone can lean against the airplane and rotate it enough to make it fall off the jacks, especially if they lean on the rear fuselage.

[carusoam]

Too add to this conversation...

I have seen bags of sand placed on the tail to add to the total down force.

Is there a reason not to do this as well?

I have seen dents in sheet metal at the "jack point" placard. The jack point is behind the sheet metal, goof ball!

We can rename this thread... "Belt and suspenders"

I get the feeling that the improper way of lifting a Mooney leads to the plane falling off the jacks more than bending something...

The jack points are close to the CG? Getting in and out of the plane while on jacks requires some thinking and checking to make sure...

What else could go awry???

Best regards,

-a-

[AmigOne]

According to Wikipedia "early in the model's history there were several incidents of wooden tails breaking up in flight due to water damage and the resulting rot". But since 1960 from the B through the J how many Mooney aircrafts have been produced with a metal tail, 3000 ? (just guessing), then 3000 times almost 50 years of annuals (SI issued 2008) would mean 150000 annuals were the tail was held down without a single identifiable incident of tail damage as a result of this procedure ?? Like I said before, I didn't do it and I will not do it again.

[Bob_Belville]

By the way Byron, it takes more than 100 pounds to hold the tail down on my C model.

David, I don't think it takes more than 100 pounds down at the tail hook to hold the nose off once the plane is on the jacks. The jack points are well forward of the main gear so it would take more to raise the nose while the plane is on the mains.

 

Bob

[Sabremech]

 I believe the issue is the fuselage and cabin sheet metal structure. I also think Carusoam is on to something with mechanics climbing in and out of the airplane while on jacks and using the tail tied down. I don't think this is something that's going to lead to the catostrophic failure of the tail section, but could lead to major repairs of the fuselage and cabin structure if the procedure is not changed.

[m20cDoug]

My C is on jacks and has been for a long time, 300# of bar bell weights on the tail stand do the job. When I put my weight on the step  the plane will rock back then resume it's tension on the shackle holding it to the stand. I also have a block of wood under the nose tire to take most of the pressure off the tail tie down since it was going on jacks long term. After reading the SI I believe that came about from the prop manufacturers not wanting the prop used as a jack point which would still put upward pressure on the engine mounts which is what the engine lifting eye also does.

[DXB]

Since the time of this thread, I've had my new to me C on jacks 3 times by two different well-known MSCs - the tail weight method was used in every case.  Justified or not, this SI's recommendations certainly doesn't seem to be catching on.   

[Bob_Belville]

1 hour ago, DXB said:

Since the time of this thread, I've had my new to me C on jacks 3 times by two different well-known MSCs - the tail weight method was used in every case.  Justified or not, this SI's recommendations certainly doesn't seem to be catching on.   

Dev, over the more than 2 years since I fabricated the weight pictured in post #1 I have used it quite a few times including most of the month of November when I extended the annual inspection to install new windows, new engine control cables, paint the nose wheel, and more. We climbed onto the wing and in and out of the cabin dozens of times. When I step on the step (I'm 220#) the tail moves down slightly due to a little slack in the hold down in the swivel screw pin clevis. The plane is very stable on jacks with this system. 

[Hector]

I have the exact same setup as Bob and use it every annual to jack up the plane. However, during annual my doghouse is off as well so just for added safety I also use a rope on the engine lift point to a steel beam on the roof of the hanger. Makes me feel a lot better as I climb in and out of the cabin during annual and it does support some of the weight so it's not all on the tail. That being said, if I need to jack the plane to check something quick at times other than annual when the doghouse is already off then I use only the washtub with concrete.

[Sabremech]

A little birdie told me the concern is the hardware that bolts the tail tie down to the aircraft. I was advised to inspect or replace the hardware if I wanted to use the tail tie down. 

It is easier and faster to use the tail tie down, but I still use a strap and engine hoist if I'm leaving my airplane on jacks for more than a few hours. 

David

Edited January 17, 2016 by Sabremech

[Guest]

And then there is this version of jacking it up.

Clarence

[DXB]

OMG - did someone use something other than the jack point here??

[Bob_Belville]

1 hour ago, Sabremech said:

A little birdie told me the concern is the hardware that bolts the tail tie down to the aircraft. I was advised to inspect or replace the hardware if I wanted to use the tail tie down. 

It is easier and faster to use the tail tie down, but I still use a strap and engine hoist if I'm leaving my airplane on jacks for more than a few hours. 

David

David! So Kerrvile got back with you and, off the record, told you the weighted tail was not a bad thing! Thanks for the followup.

Confession is good for the soul.