No back spring in landing gear actuators

[jetdriven]

Okay, now we're getting somewhere.  Some people like to keep repeating the same thing enough times until somehow there's a cobtriversy over what is or is not required to be done for airworthiness.  

[jetdriven]

On February 5, 2015 at 10:53 AM, M20S Driver said:

Please see the image from the maint manual below:

 

 

sbm20-282-a.pdf

What is the title of that chapter, Chapter 5?

[co2bruce]

We purchased our Eagle with just over 1000 hours. At the first annual at Premier we did inspect the gear back assembly and there were noticeable metal shavings in there. They called us, we went down and looked at the shavings and replaced the parts needed. I believe it was a time limit part at that time, but even if it's not you should get in there and look at it. With ours, failure was inevitable at some time and it's not a part you want to malfunction if needed. Sometimes I am amazed at the CB attitude some on this board are so proud of. This is an expensive hobby, your lives as well as your families (as well as innocents on the ground) are at risk. Please be careful out there. I am a Mike Bush student and believe if it's not broke don't touch it, but look at it and make sure, if it's broken or wearing out .......

[Cyril Gibb]

In the service bulletin, it says Mooney was informed of an actuator failure where the electrical and manual extension failed.  The implication is a failure of the no back spring, but it doesn't say that explicitly. 

Have ANY other no back springs after inspection shown cracking?  If so, within a given date range?  The SB says that current inventory of the springs should also be checked for cracks.  Have any of those shown cracking?  Is a spring with 1000 hours in service and no sign of cracking any more likely to fail than one just out of the manufacturers shop?

Disassembly of the actuator is a reasonably invasive procedure filled with various cautions and potential reassembly errors.  I'd want a clear and definitive answer to those questions before it's possible to know the relative risks of inspecting/replacing vs leaving it alone.

[carusoam]

Springs are an interesting material science.  

Giving some background from old fuzzy memory...

1) one set of heat treating conditions is used to make the spring springy.

2) another set of heat treating conditions on the end of the springs allows them to be shaped and changed.

3) the metal alloy is important to get right.

4) the heat treating steps are important to get right.

5) brittleness is a side effect of springiness.  

6) Cracks and their propagation are detrimental to the strength of the spring and leads to it's failure.

7) serialized production is an adequate procedure to produce and distribute proper parts to the field, and recall them when neccesary.

Do we have any metals, materials or spring experts here?  (I am only a PP)

I learned this spring process watching a CB mechanic working on an automobile.  The end broke off the spring.  Heating it to red hot, using pliers he bent a new loop to mount the spring.  Cool and then mount.  

- Don't heat the whole spring or it doesn't work. 

- Don't not heat the spring or it cracks and breaks.

- time, cycles and environment all contribute to the age and wear of the spring.

Hope this information can inspire more conversation regarding the failure modes for the no back clutch spring...

there are a handful of metals, alloys and heat treating parts in airplanes that have been botched through the years... (Is this just another of the same?)

Best regards,

-a-

 

[mike_elliott]

2 hours ago, Cyril Gibb said:

In the service bulletin, it says Mooney was informed of an actuator failure where the electrical and manual extension failed.  The implication is a failure of the no back spring, but it doesn't say that explicitly. 

Have ANY other no back springs after inspection shown cracking?  If so, within a given date range?  The SB says that current inventory of the springs should also be checked for cracks.  Have any of those shown cracking?  Is a spring with 1000 hours in service and no sign of cracking any more likely to fail than one just out of the manufacturers shop?

Disassembly of the actuator is a reasonably invasive procedure filled with various cautions and potential reassembly errors.  I'd want a clear and definitive answer to those questions before it's possible to know the relative risks of inspecting/replacing vs leaving it alone.

CarolAnn Garratt had one fail in Singapore. In fact, on one of her book covers is a pic of her plane with the wheels half extended over Singapore. Tom Rousch I believe fixed her up via lotsa AMU's to fedx

[M20S Driver]

9 hours ago, jetdriven said:

What is the title of that chapter, Chapter 5?

CH 5:  Time Limits/Maintenance Checks in Maint Manual.

[Cyril Gibb]

2 hours ago, mike_elliott said:

CarolAnn Garratt had one fail in Singapore. In fact, on one of her book covers is a pic of her plane with the wheels half extended over Singapore. Tom Rousch I believe fixed her up via lotsa AMU's to fedx

I remember that.  I must have too much time on hands lately, 'cause I just read the part of her journal that covered the gear issue.  The gear circuit breaker popped with the gear half down.  After resetting the circuit breaker, the gear went down and stayed locked.  She then flew a few days with the gear extended to get to a shop in Australia that disassembled the actuator and found a broken no-back spring.  So it does happen.

However, a much more interesting fact.  She had the "old" no-back spring with her that the shop then used to repair the actuator.  So it appears that she had a new no-back spring installed, which then failed.

Doesn't sound like replacing the old spring worked for her.  Same questions regarding risk, I guess.  One has to wonder how many Mooneys out there have had their old springs replaced with the same batch as hers.

[Guest]

One of the problems with the gear actuators installed in a Mooney is the normal and manual systems rely on the same mechanism.  My brand P (I'm not allowed to name it) is able to disconnect the actuator from the retraction system thereby allowing for complete manual extension of the gear.

Clarence

 

[mike_elliott]

Just now, M20Doc said:

One of the problems with the gear actuators installed in a Mooney is the normal and manual systems rely on the same mechanism.  My brand P (I'm not allowed to name it) is able to disconnect the actuator from the retraction system thereby allowing for complete manual extension of the gear.

Clarence

 

Your mother taught you well, Clarence

[Guest]

Just now, mike_elliott said:

Your mother taught you well, Clarence

I don't want to offend some of the more sensitive readers by mentioning it by name.  Besides it may not want to be mentioned here!

Clarence

[mike_elliott]

2 minutes ago, M20Doc said:

I don't want to offend some of the more sensitive readers by mentioning it by name.  Besides it may not want to be mentioned here!

Clarence

its probably ok, much better than the Asp3n word....

[Guest]

Just now, mike_elliott said:

its probably ok, much better than the Asp3n word....

If they're bad should I have it removed from P?

Clarence

[mike_elliott]

Remove the A&P, you'll be in a better place

[Cyril Gibb]

2 hours ago, M20Doc said:

If they're bad should I have it removed from P?

Clarence

Yes, and swap them (evenly) for my vacuum stuff.....

[Guest]

1 hour ago, Cyril Gibb said:

Yes, and swap them (evenly) for my vacuum stuff.....

Cyril,

I would but with limited horse power available I don't think I can carry heavy vacuum instruments.

Clarence

[M20S Driver]

14 hours ago, co2bruce said:

We purchased our Eagle with just over 1000 hours. At the first annual at Premier we did inspect the gear back assembly and there were noticeable metal shavings in there. They called us, we went down and looked at the shavings and replaced the parts needed. I believe it was a time limit part at that time, but even if it's not you should get in there and look at it. With ours, failure was inevitable at some time and it's not a part you want to malfunction if needed. Sometimes I am amazed at the CB attitude some on this board are so proud of. This is an expensive hobby, your lives as well as your families (as well as innocents on the ground) are at risk. Please be careful out there. I am a Mike Bush student and believe if it's not broke don't touch it, but look at it and make sure, if it's broken or wearing out .......

I agree completely co2bruce....  

One side of my spring showed edge deterioration.  I am not an expert to predict the failure mode and life left in the spring.  But the damage was visible!

I have a lot of respect for the legendary mechanics at the MSCs near me and in their opinion, it would be the safest to have it replaced.  I also a Mike Busch student and read his book (Manifesto), but will not take a chance in this case. I will pay the $2k even if it improves the the safety slightly.  

I don't buy that opening and servicing the actuator by a Mooney veteran and using a newly fabricated spring with all the metallurgical and inspection technology advancements will be risky. 

[jetdriven]

12 hours ago, M20S Driver said:

CH 5:  Time Limits/Maintenance Checks in Maint Manual.

So, not the "Airworthiness limitations" section.  These are two different things here. 

[cnoe]

13 hours ago, M20S Driver said:

... using a newly fabricated spring with all the metallurgical and inspection technology advancements ...

Playing devil's advocate here...   To which technological advancements do you refer? The same one's that Lycoming used in producing the new disintegrating camshafts?

My no-back-spring was already replaced once, and I'm not sure I'm going to do it again just because I'm coming up on 3,000 TTAF.

If y'all later read about me performing a GUL then I guess you'll have the last laugh.

IMO spending the 1-2 AMUs on a new AOA system would enhance safety more dramatically than replacing a spring that has few documented accounts of failure.

[M20S Driver]

32 minutes ago, cnoe said:

IMO spending the 1-2 AMUs on a new AOA system would enhance safety more dramatically than replacing a spring that has few documented accounts of failure.

I agree that AOA is worth adding.  As I am on final approach to my home airport (2400- feet runway), it would be great to set up my approach speed with AOA, and as I reach to lower the gear, it would be great to know that it was overhauled after 17 years of use and 1100 hours 

[HopePilot]

Is replacing the back spring something a run of the mill A&P can perform, or is this something best left to a Mooney-specific shop?

[kortopates]

Is replacing the back spring something a run of the mill A&P can perform, or is this something best left to a Mooney-specific shop?

Best left to someone who is experienced with it and the SB. More than the spring may need servicing as well.

Sent from my iPhone using Tapatalk

[Cardinal767]

Just purchased a M20K last August and I'm new to Mooneys. After reading about the actuator issue I just ordered the SB kit last week. Got a call from the shop today letting me know Mooney is unable to get the springs from the vendor for another 6-8 weeks. The warning signs of a possible failure is a ratcheting sound from what I read, is this during normal operations of the gear or with the emergency extend? The aircraft I purchased has 1500 hours total airframe time and nothing has been done with the actuator since new in 1981. I used my phone to record a video of the emergency extension. There is a noise made almost every time the cable is pulled. No noise in normal operations. I commute from Texas to Denver ever week, I'd like any advise on what to look or listen for until I get the parts in.

[Deb]

Don Maxwell is well respected and will be able to give you expert advice. He is very generous with his time, and would answer a phone call or email.

[donkaye]

FWIW, the back spring being a single source of failure, means your gear will neither come up or go down in normal or backup mode if the spring fails.  I have replace mine every 1,000 hours until there were no more back springs made for the Plessy Gear Actuator.  The last spring for the Plessy cost $1,500 for the spring alone.  I watched Tom Rouch take the actuator apart and replace the spring.  It took him 3 hours.  I  WOULD ONLY HAVE AN EXPERIENCE PERSON DO THE REPLACEMENT.

Since there were going to be no more back springs available, Tom made up a new gear actuator for me with springs that ARE available.  The cost of the actuator was much less than a new one priced at $18,000.  Typical rebuilt ones cost around $10,000.  Mine was much less than that.

Bottom line for me is that unlike Mike Bush's replace as needed philosophy, in this case I would stick to the recommended 1,000 hour replacement time.  I'd hate to see an expensive airplane need $50,000 in repairs from a gear up landing when a $500 back spring could have saved it.