No back spring in landing gear actuators

[Sabremech]

32 minutes ago, M20Doc said:

I can’t imagine many companies wanting to produce these springs.  The first lawsuit after a gear up landing would seal their fate.

Clarence

If we thought solely about that, we wouldn’t be involved in anything aviation. 
David

[N201MKTurbo]

After talking with the FAA lady that approves all things PMA around here, an entity could write all the quality documents and FAA documents to get the PMA. They don’t actually have to manufacture the part, they just have to assure it complies to the design docs. They could sell it and take all the liability without making anything.

[philip_g]

How hard is it to get a pma based on identicality? I can very very easily get these made.

Edited November 16, 2021 by philip_g

[EricJ]

12 hours ago, N201MKTurbo said:

After talking with the FAA lady that approves all things PMA around here, an entity could write all the quality documents and FAA documents to get the PMA. They don’t actually have to manufacture the part, they just have to assure it complies to the design docs. They could sell it and take all the liability without making anything.

I think that's how many/most PMAs are done.    Even if somebody is doing a value-add change to something, or integrating a few parts, much or all of the basic item is often sourced elsewhere.   The Mooney factory probably never made these springs, or the gear actuators, etc., etc.

 

[EricJ]

4 minutes ago, philip_g said:

How hard is it to get a pma based on identicality?

How hard is it to prove "identicality"? 

That said, even when I was engineering avionics for airliners it was fairly routine to ask for "qualification by similarity" for new parts or products that did the same or similar thing as previous items, in order to be able to re-use previous qualification effort.

Edited November 16, 2021 by EricJ

[philip_g]

3 minutes ago, EricJ said:

How hard is it to prove "identicality"? 

That said, even when I was engineering avionics for airliners it was fairly routine to ask for "qualification by similarity" for new products that did the same or similar thing as previous items, in order to be able to re-use previous qualification effort.

 

FAA term. Not mine.

https://www.faa.gov/aircraft/air_cert/design_approvals/pma/pma_des/

Might be easiest to figure the specifications and share them so people can use example one and have their own part produced, if no one with a pma gets it  done.

Edited November 16, 2021 by philip_g

[EricJ]

1 minute ago, philip_g said:

FAA term. Not mine.

https://www.faa.gov/aircraft/air_cert/design_approvals/pma/pma_des/

 

That says if you have a license agreement to produce the part that that can be used as evidence of identicality.   Without that you still have to show that it is "the same in all respects" to the original item.   The open-endedness of that statement is often a stumbling block.   Even if only a few parameters matter in the design, it may be easy for someone to claim that many more parameters that don't matter but are difficult to prove are required.   It looks like the FAA assumes that the presence of a license agreement suggests that the licensor has assured that all the important parameters are covered in the agreement.

Hence my question, how hard is it to prove "identicality"?    It often seems to be a moving target.

[philip_g]

6 minutes ago, EricJ said:

That says if you have a license agreement to produce the part that that can be used as evidence of identicality.   Without that you still have to show that it is "the same in all respects" to the original item.   The open-endedness of that statement is often a stumbling block.   Even if only a few parameters matter in the design, it may be easy for someone to claim that many more parameters that don't matter but are difficult to prove are required.   It looks like the FAA assumes that the presence of a license agreement suggests that the licensor has assured that all the important parameters are covered in the agreement.

Hence my question, how hard is it to prove "identicality"?    It often seems to be a moving target.

With a spring how much is there to prove? If you prove its dimensionally the same and the same material I can't see what else they could ask for? I guess they could ask about heat treatment.I guess I can't see it being worth the headache to sell 5 springs.

Edited November 16, 2021 by philip_g

[EricJ]

2 minutes ago, philip_g said:

With a spring how much is there to prove? If you prove its dimensionally the same and the same material I can't see what else they could ask for? I guess they could ask about heat treatment 

The spring constants would be pretty important, I think torsion in this application.   Materials, like "exact" alloy, heat treatment, etc., etc., get harder to prove, and harder to know what the original engineering effort had in mind or thought was important.   Using the expertise of an experienced spring fabrication shop would likely get you what you needed for a practical reliable part, but satisfying somebody else's requirement for "identicality" might be the harder task.   I say this not ever having tried to get PMA approval for anything, but this is usually where the criticism goes even when suggesting OPP, which is a lower bar since it is single use.   Perhaps the FAA PMA authorization process is more practical than internet OPP critics. 

[N201MKTurbo]

4 minutes ago, philip_g said:

With a spring how much is there to prove? If you prove its dimensionally the same and the same material I can't see what else they could ask for? I guess they could ask about heat treatment.I guess I can't see it being worth the headache to sell 5 springs.

There is more than just the materials. Springs are typically heat treated (hardened) and then tempered. 

I found a spring company that will do short runs and has the aerospace quality system in place. They specialize in wrap spring clutch springs. I think the amount of torque transmitted through the clutch would be important. 

The FAA would probably be a bit more lenient when reproducing an abandoned part. I think if you could put together a test setup using the same assembly as the actuator clutch and loaded it up to its operating torque for a couple of thousand cycles, that would probably make them happy.

[Marker89]

On 11/9/2021 at 12:02 AM, Sabremech said:

I do have PMA and am willing to support the Mooney fleet in those parts that it makes sense to get PMA on. I’m also willing to help as far as owner produced parts where it doesn’t make sense to go as far as PMA.

Thanks,

David

Hi David 

 

Do you happen to have a phone number and an email that I can use so that I can contact you directly? I have been looking in to the "No back" Springs as a customer of ours is in need of one and I have seen you mention that you have a PMA, I'd just like to talk further to you about it and see if this would be a good path for us to go down!

[Pinecone]

I think a number of people in the Mooney world would be willing to buy one to have on the shelf.

[1980Mooney]

29 minutes ago, Pinecone said:

I think a number of people in the Mooney world would be willing to buy one to have on the shelf.

You really think people would buy an unproven spring?  One that, if it breaks while retracting the gear, the gear will not go down for landing.   That will insure a gear-up landing and in this market, down for a year,  that is if the insurance company doesn't scrap the plane.

If I was looking to buy a plane that the Logs showed had an OPP or "Off Brand X" no-back spring, the deal would have to be contingent on the Seller replacing the spring at their expense.

Just my 2 cents.

[PT20J]

44 minutes ago, 1980Mooney said:

You really think people would buy an unproven spring?  One that, if it breaks while retracting the gear, the gear will not go down for landing.   That will insure a gear-up landing and in this market, down for a year,  that is if the insurance company doesn't scrap the plane.

If I was looking to buy a plane that the Logs showed had an OPP or "Off Brand X" no-back spring, the deal would have to be contingent on the Seller replacing the spring at their expense.

Just my 2 cents.

If it is a true PMA part, it will have gone through FAA Design Approval to show that it is identical or equivalent to the original.

https://www.faa.gov/aircraft/air_cert/design_approvals/pma/pma_des:

"The design approval phase of PMA certifies that a replacement or modification article complies with the airworthiness standards of eligible products (aircraft, engine, or propeller). The applicant shows this compliance through tests and computations unless the article is identical to the article design on a type-certificated product. Identicality means that an article is the same in all respects to an article design in a type-certificated product. Evidence of license agreement shows this identicality."

[GeeBee]

2 hours ago, 1980Mooney said:

You really think people would buy an unproven spring?  One that, if it breaks while retracting the gear, the gear will not go down for landing.   That will insure a gear-up landing and in this market, down for a year,  that is if the insurance company doesn't scrap the plane.

If I was looking to buy a plane that the Logs showed had an OPP or "Off Brand X" no-back spring, the deal would have to be contingent on the Seller replacing the spring at their expense.

Just my 2 cents.

Given the history of defective factory springs, how much worse could it get?

[PT20J]

37 minutes ago, GeeBee said:

Given the history of defective factory springs, how much worse could it get?

There are thousands of Mooneys with these springs and millions of gear operations and only a handful of documented failures mostly in Plessey actuators. The Eatons seem pretty sound except for maybe one bad lot of springs maybe 30 years ago. 

I think this is like the dual mag - everyone worries about it out of proportion to the risk. Historically, pilots are many times more likely to belly in because they didn’t put the gear down than to have a mechanical failure of the actuator.

Skip

[A64Pilot]

3 hours ago, 1980Mooney said:

You really think people would buy an unproven spring?  One that, if it breaks while retracting the gear, the gear will not go down for landing.   That will insure a gear-up landing and in this market, down for a year,  that is if the insurance company doesn't scrap the plane.

If I was looking to buy a plane that the Logs showed had an OPP or "Off Brand X" no-back spring, the deal would have to be contingent on the Seller replacing the spring at their expense.

Just my 2 cents.

You wouldn’t see that in the entry.

What you most likely would see was replaced no back spring, serviced and lubed actuator, tested reinstalled and rigged.

If it was an OPP then you should see that but not necessarily for a PMA part.

Most of the times you have to read between the lines, my “no damage history” 140 has a logbook entry where one wing was replaced. Almost certainly it was ground looped and the wing replaced due to damage, but it doesn’t say that, just says replaced.

Now days owners are told anything negative they must get put on a sticky, and don’t put that sticky in the logbook, and then told they are only required to keep the sticky for one year, obvious implication is after one year throw the sticky away, my belief is most don’t wait the year.

So what are logbooks worth now?

[GeeBee]

I can name about 50 items on the PA-18 line of aircraft which are PMA'd and much better than the original. McFarlane has made a business out of PMA'd parts that are better designed and more durable than original, everything from door hinges to landing gear saddles to gascolators. Same with Atlee Dodge. To quote one instance, ECi as an example, well I can quote 2 successes for every failure. Spring manufacturing is not rocket science. If someone shows me why their PMA'd spring is better, and has data to back it up (which is not hard to obtain), I'm in.