No back spring

[John Mulvey]

I have a 1984 J model and our mechanic is insisting my no back spring should be changed due to a service bulletin.  
My reading finds that the bad batch of these came out about 6 years after my plane was assembled. So I should have a good spring.  
If the spring DOES fail, will the emergency lawn mower pull gear extend still work? 

[toto]

No. If the spring fails, it takes out the emergency extension mechanism too.

There’s a ton of good discussion on MS about the NBS.

[mike_elliott]

John, if it is determined you need one, LASAR was kind enough to donate one to the Mooney Summit Silent auction. At first glance, it appears it was not bid on and would be available. @toto is correct, your spring breaks, your next purchase is a ferry prop rental and some belly skins. (opps, my bad the 84 J is the year they put on the nicer one piece belly skin) What your really asking is it necessary to change out a part that isnt broke (yet) and of course the answer is It depends. The SB was put out for a reason, as these lil guys do break and do have a life of having their little tangs pulled on. If you decide to go for it, let me or Alex know and we can get it to you.

Congrats on winning the Mooney Mover Tug!

Another unsold item is a JPI Fuel scan 450 and a John Liskey custom painting of your aircraft.  if anyone would like to purchase these great donations to the Mooney Summit to aid downed Mooney Pilots families, let me know, I know a guy who knows a guy and can get them to you.

[EricJ]

Service Bulletins are not mandatory for private use under Part 91.    The no-back springs are very expensive to replace and do not have a significant history of failure over the history of their use in Mooneys, so most people don't bother with changing them.

If your A&P insists on performing every Service Bulletin as though it's mandatory your ownership experience is going to be very expensive.

[Fritz1]

This has been discussed ad infinitum, think Don Maxwell said if it does not rattle, don't replace it, lubing the actuator per service manual is a good idea, I have never seen a broken spring and do not know anybody who had one break, think the part is $2500 and the labor typically runs at $800

[PT20J]

When talking about no-back springs, it is important to distinguish between the two actuator manufacturers that Mooney used. There have been a number of documented failures of springs in GEC/Plessey actuators and I do not believe that no-back springs are available for these. The Eaton actuators (which confusingly were manufactured under several names) seem more robust. There was at least one (maybe two) documented failures many years ago causing Eaton to recall certain serial numbers which I believe is the source of the idea that there was a bad batch of springs. Probably some of these were never pulled and sent back to Eaton, but if they were going to fail, they'd certainly have done so by now.

The spring is a wrap spring brake/clutch and it will wear in service. The chattering that Don Maxwell speaks of as a symptom of needing replacement is undoubtably caused by slippage of a worn spring. 

Outright failure is caused when the tangs on either end of the spring break jamming up the mechanism. I think this is a very, very unlikely event and I'm in no hurry to replace mine given the possibility of a maintenance-induced failure especially since there are now very few mechanics that have any significant experience working on these things. But, each owner will need to assess the risk and chose a course of action that they believe appropriate.

[cliffy]

IIRC they found maybe 2 broken springs from one batch and it was traced to a bad heat treat of that batch.

Small cracks on the tightest bend of the spring that lead to failure 

I think the SB was a CYA to cover failures in that batch of springs at the time. 

We didn't have and replacements for years and the sky did not fall in on the Mooney fleet but each owner will have to make their own determination of what SERVICE BULLETINS he wants to do as they are not mandatory for Pt 91 operations. 

ADs are another matter.

If your maintenance shop does a lot of repairs on Pt 135 charter airplanes they may be more inclined to want SBs 

done as its  mandatory for Pt 135 to do them all. 

To replace it is a significant expense and not many shops today even know how to do it.  Pick a good one if you decide to do it. One with experience preferably. 

[hazek]

3 hours ago, cliffy said:

IIRC they found maybe 2 broken springs from one batch

This is being repeated over and over again and yet there is a SB M20-282A that calls for the spring to be replaced after 1000h. Maybe the reason we're not getting more of these failures is people are actually replacing these springs sooner rather than later?

[PT20J]

12 minutes ago, hazek said:

This is being repeated over and over again and yet there is a SB M20-282A that calls for the spring to be replaced after 1000h. Maybe the reason we're not getting more of these failures is people are actually replacing these springs sooner rather than later?

There were a couple of Plessey failures at around 1000 hours. That may be the origin of the 1000 hour requirement - I don't know for sure. Keep in mind that the 1000 hour mandatory replacement applies to both Plessey and Eaton actuators. Don Maxwell told me that he understood that the Eaton spring was rated for something like 20,000 operations. 

[1980Mooney]

2 hours ago, PT20J said:

There were a couple of Plessey failures at around 1000 hours. That may be the origin of the 1000 hour requirement - I don't know for sure. Keep in mind that the 1000 hour mandatory replacement applies to both Plessey and Eaton actuators. Don Maxwell told me that he understood that the Eaton spring was rated for something like 20,000 operations. 

So let's say on average you cycle the gear five (5) times every hour over the life of a plane - that means it should last 4,000 hours......

I seems reasonable that is what the engineers were thinking when they designed it.

[N201MKTurbo]

46 minutes ago, 1980Mooney said:

So let's say on average you cycle the gear five (5) times every hour over the life of a plane - that means it should last 4,000 hours......

I seems reasonable that is what the engineers were thinking when they designed it.

Who cycles their gear 5 times an hour? Are you using it for primary training? 

[toto]

1 minute ago, N201MKTurbo said:

Who cycles their gear 5 times an hour? Are you using it for primary training? 

That’s roughly my understanding of where the 1000 hour guidance came from. Since Mooney owners aren’t tracking cycles, they just track hours and use a “primary trainer” worst-case scenario for cycles per hour. 

Before the most recent factory closure, I had heard rumors that the SB was being updated to 2000 hours as a guideline, on the basis that it was a more realistic but still very conservative number.  Dunno. 

[1980Mooney]

58 minutes ago, N201MKTurbo said:

Who cycles their gear 5 times an hour? Are you using it for primary training? 

If an engineer is using worst case then they would assume that.  Let's not forget that long ago, Mooney's were used for training.  Does anyone remember the "AT"?  GMAX has one for sale now.  I seem to recall a few years ago there was one in Asia used by an airline for training.  It was imported into Canada I think with something like 10,000 hours.

1990 MOONEY M20J AT For Sale in Spring Branch, Texas | www.gmaxamericanaircraft.com   (This is a former instrument trainer (it was an 'AT' when new).

[0TreeLemur]

Nice thread here-

[cliffy]

On 9/17/2025 at 3:40 PM, hazek said:

This is being repeated over and over again and yet there is a SB M20-282A that calls for the spring to be replaced after 1000h. Maybe the reason we're not getting more of these failures is people are actually replacing these springs sooner rather than later?

There are some of us who were around when this SB came out and remember the background of what actually happened. Even though it was only a couple of springs that went bad due to a bad heat treat in a batch of springs, the risk factor of the gear up landing if one was to break again (think lawyers) was high enough to make the 1000 hrs  change out a reality. This would also preclude changing the SB to longer time limit today with today's litigious society. 

If it was an inherent problem with the design and wear factors of the spring itself we would have seen springs failing many times in the years before this SB came out. What changed?  What have we done now when the springs were not available for years? We flew and didn't have spring failures. 

Many Mooneys would have had gear up landings because many Mooneys had more then 1000 hrs on the spring they came with before the SB.

Fleet average might realistically be 1 or 2 gear operations per hour given 4000 hr airframes only 8000 operations over 40 or more years. Is there a limit to how long a god spring will last? We don't have those numbers so it seems reasonable to change the spring at some time down the road. I'm sure Al Mooney never figured his designs would be flying 60+ years after they left the factory. 

SB's are, after all, "optional" for Pt 91 airplanes (Australia aside :-)  Your choice.

Can anyone report on any Mooney gear failure due to a back up spring failure recently? Please provide the details so I can research the issue.

Due to the very detailed SB requirements this is a prime place for "maintenance induced failures" if not done exactually like the SB proscribes. Being as esoteric as this particular maintenance action is it is not one to be attempted by just any A&P. 

Do I dare say "Johnson Bar" anyone  :-)

[PT20J]

9/15/91 Lancaster, PA M20J: UNABLE TO RETRACT GEAR ON CLIMB. EXTENDED GEAR AND LANDED. GEAR ACTUATOR WAS JAMMED DUE TO CLUTCH SPRING FAILURE. FAA AIDS report number 19910915046159I

7/5/03 Oxford, CT M20R: WHILE ON FINAL APPROACH THE GEAR FAILED TO EXTEND. PILOT DIVERTED TO WATERBURY OXFORT AIRPORT IN CT, WHERE HE LANDED GEAR UP. INVESTIGATION REVEALED THAT THE LANDING GEAR ACTUATOR "NO BACK SPRING" HAD A BROKEN TAB WHICH CAUSED THE ACTUATOR TO MALFUNCTION. FAA AIDS report number 20030705013639I

10/30/03 Toms River, NJ M20S: LANDING GEAR WOULD NOT EXTEND. PILOT LANDED GEAR UP. THE AIRCRAFT WAS JACKED AND THE GEAR TESTED IN NORMAL AND EMERGENCY SYSTEMS. GEAR WOULD NOT MOVE IN EITHER POSITION. DISASSEMBLED THE LANDING GEAR ACTUATOR. FOUND THE TABS HAD BROKEN OFF THE NO BACK CLUTCH SPRING PREVENTING THE GEAR FROM MOVING IN EITHER THE NORMAL OR EMERGENCY POSITION. FAA AIDS report number 20031030030799I

6/12/22 Charleston, SC M20J. This was classified as an accident and investigated by the NTSB because of substantial damage to the structure during the gear up landing. The failed spring had been replaced nearly 5 years and 427 hours earlier. Probable cause: THE FAILURE OF THE TORSION SPRING (Note: This was a Plessey actuator. Eaton calls the part a "no back spring" but Plessey calls it a "torsion spring") INSIDE THE DRIVE CLUTCH ASSEMBLY OF THE LANDING GEAR ACTUATOR WHICH PREVENTED NORMAL AND MANUAL EXTENSION OF THE LANDING GEAR. NTSB accident report number ERA22LA319

[MikeOH]

Interesting....four gear-ups due to no-back spring failure in 4 decades.

How many gear ups in those 4 decades due to no brain?

[varlajo]

2 hours ago, MikeOH said:

Interesting....four gear-ups due to no-back spring failure in 4 decades.

How many gear ups in those 4 decades due to no brain?

Well in all honesty there is a mandatory biannual IRAN procedure for the contents of the brain.. 

Edited 5 hours ago by varlajo