John Mulvey Posted Monday at 11:23 AM Report Posted Monday at 11:23 AM 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 Posted Monday at 11:53 AM Report Posted Monday at 11:53 AM 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 Posted Monday at 12:23 PM Report Posted Monday at 12:23 PM 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 Posted Monday at 01:54 PM Report Posted Monday at 01:54 PM 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. 8
Fritz1 Posted Monday at 11:29 PM Report Posted Monday at 11:29 PM 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 Posted Tuesday at 03:56 AM Report Posted Tuesday at 03:56 AM 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. 8
cliffy Posted yesterday at 06:29 PM Report Posted yesterday at 06:29 PM 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 Posted yesterday at 09:40 PM Report Posted yesterday at 09:40 PM 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 Posted 23 hours ago Report Posted 23 hours ago 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. 1
1980Mooney Posted 21 hours ago Report Posted 21 hours ago 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. 1
N201MKTurbo Posted 20 hours ago Report Posted 20 hours ago 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? 1
toto Posted 20 hours ago Report Posted 20 hours ago 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. 1
1980Mooney Posted 19 hours ago Report Posted 19 hours ago 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).
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