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Topic-icon Cracks in webbing of main landing gear trunnions

  • Pete Castine
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3 months 1 week ago #1416

I have a 1971 P28R Cherokee Arrow. Annual time rolls around, and there seems to be a new issue every year! The life of an aircraft owner?

The IA noticed cracking in the paint of the main gear trunion webs. Stripped and dye-tested, and confirmed there are some small stress fractures forming.

Question 1: is there any guidance from Piper as to what may be acceptable, or is the mere presence of cracks deem the aircraft un-airworthy? IA contacted Piper, no answer yet.

Question 2: obviously I’m not going to wait for these to get worse; any advice where I can find new (ha! Probably not) or refurbished trunnions (both mains) for a 1971 P28R?

Thanks for any insight,
Pete

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3 months 3 days ago #1423

Hi Pete;
Sorry for the tardiness of this reply. One bulletin that might apply is SB 292 Landing Gear Modification, PA-28R-180. I do not have a copy of it.
I couldn't find any other Piper publication addressing cracking the MLG trunnions on your PA 28R. However, there have been cracking noticed from a tooling hole in the MLG trunnion of PA 24 Comanches. The experts advise smoothing and polishing the edges of the hole so a smooth surface is presented. Cracks are much less likely to develop in a surface without sharp edges.
If you have to look super closely to detect the cracks, you may be seeing very small surface cracks that don't compromise the strength of the structure. Tiny cracks can be polished out without compromising the airworthiness of the part.
You can email Piper by sending a request to: .
The decision to attempt to polish out tiny cracks will rest with your mechanic. Some mechanics will take the initiative in situations like this to do a little exploring; while others want a directive from the manufacturer before they attempt this type of investigation.
As far as finding new trunnions, you should be able to approach any of the aircraft salvage yards in the country with your request. It's to your advantage to go to the companies with part numbers.
If you'll tell me the year and serial number of your airplane, I'll see if I can find the correct part numbers.

The following user(s) said Thank You: Richard Easterwood

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  • Pete Castine
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3 months 3 days ago #1426

Hi Steve,

Thanks for your help; I really appreciate it. My Arrow is a 1971 S/N P28R-7135208.

Here are some pictures of the MLG trunnions.



The part numbers are:
67926-00 TRUNNION ASSEMBLY - Main gear, left 1
67926-05 TRUNNION ASSEMBLY - Main gear, right 1
My first goal would be to save these parts; as you can see the cracking is very minor. Considering the amount of material to be removed as your diagram showed, removal of some material from these to dress the cracks should be inconsequential. We will contact Piper (again) to get their take - we contacted them previously but had no response.

In addition, the Arrow requires a removal and inspection every 500 hours of the main sidebrace bracket assembly to comply with an AD. My time has come...and apparently it’s a bit of a job to remove these brackets. My A&P mentioned that if the brackets are replaced by those from a PA-32, then they will not require inspection again. The part numbers he provided me are: P/N 95643-06 / -07 /-08 / -09. I’ve found some new, but they are over $2,000 each! Any assistance locating some reasonably priced alternatives would be greatly appreciated.

Thanks,
Pete

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3 months 1 day ago #1436

Hi Pete;
I suggest you remove the sidebrace stud brackets--it's an easy task in my PA24 which is also affected by the same sidebrace stud inspection as your PA 28R. Then remove the stud from the brackets and get your mechanic to find a shop that can do the fluorescent penetrant inspection or the magnaflux inspections called for in the AD. If there are cracks then you have to get a new larger stud and modify the brackets per the AD, or buy new studs and brackets.
The initial inspection does not require the purchase of anything. There may be a machine shop near where you live that can do either the fluorescent penetrant or the magniflux inspection needed. I believe all aircraft engine shops have the tooling to perform the magnaflux inspections.
If you don't find any cracks, re install the stud in the brackets and re install. Fly for another 500 hours and repeat. There were no cracks in either of my studs.
As far as buying parts cheaper, that's not as easy as it once was. Piper now sells its parts through Aviall, a national parts house. You may find the parts you need through an internet search, or used from a salvage yard but they will have to be inspected in accordance with the AD prior to installation.

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3 months 17 hours ago #1438

You can buy the new 5/8" stud ( 78717-02) and bushing (67026-12), along with the washers, roll pin and nut for around $700.00. A good machine shop should be able to ream and chamfer your bracket to accept the new parts.

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2 months 2 weeks ago #1451

Don't forget that you get access to free parts locating with your membership. You can access the form here and Kent will get to work to locate parts at the best price available.
You can fill out the form here: www.piperflyer.org/members/parts-locating.html

Jen

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