Menu Sign In Contact FAQ
Banner
Welcome to our forums

Proposed AD for PA-28 wing spars

https://www.aopa.org/news-and-media/all-news/2018/december/20/faa-proposes-airworthiness-directive-on-piper-wing-spars

This is of course the proposed response after the Embry Riddle Piper Arrow lost a wing.

Andreas IOM

Is an eddy current inspection of the wing roots really that cheap? 300 dollars per aircraft?

Biggin Hill

I had it done in July. The NDT testing company charged £ 387 – (this was 50% of what they billed for the afternoon as an Arrow was done on the same day. We shared the cost).

Then £ 147 labour to the Engineers to remove the 4 bolts, replace them with new and check the torque on the remaining bolts. New bolts and washers were circa £ 20.00
I thought this cost was very reasonable.

I don’t believe that the average A&P in the US or engineering facility in the UK will have a bolt hole probe or the trained staff to operate it so they will have to bring somebody in. The costs in the FAA’s consultation sees very optimistic to me. I doubt you would replace a main spar in 32 hours for example. After you have drilled out hundreds of rivets the wing would need respraying and all sorts.

I do agree it is sensible to do however. At least I got in before the rush!

United Kingdom

Imho the core question (as with many such inspection procedures) is, if pulling the bolt of a decades old plane where the bolts have never been touched can cause more damage than the risk of an actual crack in the spar. That is tricky to answer.

This thought might also be the reason, why the FAA according to the draft AD thinks that it is a good idea to spend 2 hrs. of document review to determine if a 1,5hr. inspection of the plane should be performed. Would be strange if there is no downside of the inspection.

From that POV there is one big caveat for the current draft: The formula for calculating “adjusted service hours” assumes, that 100hr. inspections are only done at planes with very high workload. That might be true for the US. In Europe I know many owners, who do a 100hr. inspection routinely before every annual. Therefore the formula leads to significantly different results…

Germany

Looking at what’s involved yesterday, it seems that the bottom bolts can be removed and the holes tested with some magic or other without stripping the aircraft. (Apart from getting the rear seat out without gouging the interior!).

What I really don’t understand is what the 5 bolts in series actually do. Since all the load is handled by the end bolt, what are the rest actually for? Insurance in case someone forgets to tighten the other 4? The failed spar broke after the end bolt, not in the middle! Sorry if this a naive question, but how can any force at all be handled by the inner 3 bolts?

I also wonder before we plunge enthusiastically into disturbing all these decades old fasteners whether we have to whole story on what actually happened in Florida? It seems very strange that a relatively new aircraft (OK, high time) could suffer so much fatigue when huge numbers of old clunkers like mine (approaching 7000 Hrs over 30 years) still hold together. It’s not a facetious question to ask after the bolt inspection, how many fretted holes/cracks/missing bolts etc. will start to occur as a result? It would be unfortunate if all this tampering with the world’s second most popular aircraft turns out to be the result of some undocumented damage or history with the the accident airplane, while in the meantime someone’s wing actually does fall off as a result of the meddling.

I wonder if a quick survey of all the currently dismantled aircraft. like the one I was looking at yesterday, might not generate a more realistic assessment of the risk, rather than fiddling with thousands of perfectly serviceable aeroplanes, some of which might suffer damage as a result. There must be at least a hundred lying around in pieces even in UK.

Finally, does anyone have an idea of when this AD might come into effect in UK, if at all? My plane is offline in annual right now for a month while I’m travelling and already has the spar/tank AD come up, so it might make sense to do the new one at the same time if it is inevitable anyway.

EGBW / KPRC, United Kingdom

The first thing is if the AD is mandated by the FAA it will automatically become an AD in Europe/ UK.

As to damaging the aircraft, his is unlikely unless there are other issues in the area.

It doesnt make sense to rush and get this done yet as it is not yet an AD. It is not clear yet what exact instructions and requirements will be as it is still a proposal and faa is collecting comments . So if you do your check now you end up risking to check it again once it become a official. So I don’t really understand why some of you had already had this done.

EDTG, Germany, Switzerland

I had it done because I own a 39 year aircraft with 9,700 hours Airframe time. I don’t know it ever had some horrible hard landings in the 35 years before I owned it. The Embry Riddle plane was much younger in age and total hours.

Removing 2 bottom bolts and sending in a NDT probe is at the less risky spectrum of causing Maintenance Induced Failures (MIF) as long as you don’t hammer the bolts out. If your engine fails you can glide down and you have a good chance of coming out alive. If a wing suddenly rips off you have no chance.

What I did is exactly in line with the proposed instructions (which are reasonably clear). We’ll have to see what the final AD says but I doubt the inspection method will change. I am guessing that if you don’t have indicated cracks then you won’t have to test again for many thousands of (factored) hours.

It gave me great peace of mind and as I am spending £15 K on a respray/window change/ tanks out/ main spar inspection panels/ other work it would be crazy to find out you had a cracked main spar with a new paint job and shiny new windows!

Even if I didn’t have the respray done I would have still done the NDT. Peace of mind is my answer!

United Kingdom

I really can’t get my head around “factored” hours…how that is calculated….anyone that can explain, so that even I understand?

ESOW, Sweden

AndersB wrote:

I really can’t get my head around “factored” hours…how that is calculated….anyone that can explain, so that even I understand?

The point is that all flight hours do not cause equal wear on the airframe — it depends on how the aircraft was used. So the number of flight hours does not correspond directly to the amount of wear. The idea behind “factored” hours is an attempt to “normalise” according to the wear so that a flight hour with much wear counts in full while a flight hour with little wear counts for less than one hour. The (proposed) AD gives a precise description of how this is calculated.

The underlaying assumption behind the calculation is that aircraft having had 100 hr-inspections — as opposed to only annuals — have been subject to more wear. So the fewer 100 hr-inspections, the fewer “factored” hours. The reasoning appears to be that 100 hr-inspections are only done by flight schools and other operations with more intensive wear. This assumption may be reasonable with the typical US maintenance regime but I doubt it applies to aircraft under a typical European maintenance regime.

Last Edited by Airborne_Again at 10 Jan 09:07
ESKC (Uppsala/Sundbro), Sweden
55 Posts
Sign in to add your message

Back to Top