Reasonably priced strut inspection

[Ed O'Brien]

Re: Reasonably priced strut inspection

Other people are more knowledgable about this than I... so disagree if I'm wrong. BUT, Luscombes and Pipers have exhibited the same issue. I think they've both had similar ADs. We shouldn't think our planes are exempt from the same laws of nature and time. However, I thought the Luscombe and Piper Ads were less onerous, yet considered thorough.
Click here for the Piper AD... there's some good background
as to reasoning:

http://www.ntsb.gov/Recs/letters/2000/A00_22.pdf

I've not found the Luscombe AD only references to it in my reading.

With regards;
ED OBRIEN

[Hank Jarrett]

Re: Reasonably priced strut inspection

Terry,
Your group has addressed the main problem. By combining two processes you get around the weakness of each! Eddie Current JUST DON'T WORK for what we need! It is for finding CRACKS, not corrosion. It will be very repeatable at looking at a crack, but is pretty worthless for corrosion (as you saw).
X-ray will show you WHERE the corrosion is, but can't quantify the depth (OK there are REALLY expensive digital X-ray systems that might be able to, but you and I aren't going to get access to them). Ultra-sonic needs a known "standard" to work from but can measure thickness with a standard. Unfortunately it only looks EXACTLY where you put the probe. If there is corrosion 1/4" to the side of your scan you will miss it. Combining X-ray and ultrasonic is a great solution to localize where you need the ultrasonic.
The big question now is, how much corrosion is too much? I still say it is vital to know how bad it has to be before you trash the strut, and THAT requires a pull test. We need to know the maximum allowed design tensile load on each strut and how much the FAA is going to require or struts to be able to carry (obviously higher than the max design load). A tension-loading device is simple and you could make one in your garage in a weekend. I STILL say, a tension test is the ONLY way to KNOW a strut isn't going to fail (under a load lower than the test). Once you know there is NO corrosion (on a really good strut), you can skip the ultrasonic test. If there IS corrosion, the FAA has to tell us how much is too much. If they say, "Yours is too much" we should pull the strut to the allowable (after clean up). If it passes the pull test, the FAA is WRONG in their "estimate" and the inspection needs to be updated, but every strut that passes a pull test and has all the corrosion removed and treated is acceptable for use. You just PROVED it with a load test. I don't see how they can argue with a pull test. It's good, because you PROVED it.
After the first inspection and test there should ONLY be an x-ray required to prove the strut condition hadn't changed. If the X-ray is the same, there is no new corrosion, and you already PROVED the strut was good with the section area that is there already.
Hank

[VictorBravo]

Re: Reasonably priced strut inspection

Please see my post regarding five local Taylorcrafts having X-ray radiography done today.... in the main "strut AD" thread. Similar results as Terry.

[dewhitaker]

Re: Reasonably priced strut inspection

I have seen first hand the weaknesses of some of the NDT testing proposed. Much is dependant on the operators ability to interpret results. Thanks for doing the testing to gather data.

I want to point out that AD 99-01-05 concerning the Piper lift struts, after outlining the NDT procedure, concludes this way: see paragraph 9 "The suspect area(s) shall be tested with a Maule "Fabric Tester" as specified in Piper Service Bulletin No. 528D or 910A"

It would seem to me that the Maule test trumps the NDT test. In my comments to the FAA I am going to lobby for the dropping of the NDT procedure and go straight to the Maule Fabric tester as the final arbitrator of airworthiness of the strut. Much more cost effective and reasonable.