Lift Strut Failure

[Scott]

I've attached the TSB report on a fatal J3 accident which perhaps, should leave us feeling thankful that the FAA imposed a far more stringent inspection requirement for Taylorcraft lift struts compared to other types in response to basically the same issue (internal corrosion of wing lift struts).

The accident aircraft had not been properly maintained and the owner/pilot was clearly irresponsible, but the key finding here is that the "punch test" prescribed in the Cub AD apparently has a low probability of revealing problems:

".....the heavily corroded area on the lower half of the failed wing lift strut assembly had a remaining wall thickness between 0.002 and 0.019 inch, well below the required minimum. Punch tests applied to this area revealed one perceptible dent.

the corroded area of the upper half of the failed wing lift strut assembly had a remaining wall thickness between 0.021 and 0.031 inch; therefore, some areas were below the required minimum. Punch tests applied to these areas did not produce any perceptible dents."


J3 Lift Strut failure a19c0026.pdf

[Robert Lees]

Scott, the URL in your post doesn't seem to work for me.

But, your attached file does. But could you add the definitive Canadian TSB link please?
Found it: https://www.canada.ca/en/transportat...h-terrain.html

EDIT: That link doesn't seem to work either, The Canadian TSB needs a better system, it would appear.



Anyway, everyone needs to look at the original Piper strut AD. That was the start of ours, and from the photo in the Cub report above, was completely ignored. Just my initial opinion. For further reading, look at "Dave Wiley" Taylorcraft crash.

[PA1195]

Truly a sad ending for all, including the airplane. During restoration we replaced the lift struts and forks on my nearly identical PA-11 (same TCDS). One to end the recurring AD's, and another to add strength to the wing support structure. When tapped and held vertical internal corrosion products were released from the old struts, similar to the FAA's SAIB CE-11-05 inspection recommendation for Taylorcraft landing gear tie strut internal corrosion.

Then there's the possibility of additional compromise from external damage due to prolonged impact contact and corrosion on the J-3's struts. Not wearing cockpit restraints and loose gear is another risk as noted. Turbulence on the flight day may have added another layer to the strut failure.

Gary

[Hank Jarrett]

I tried to get the FAA engineers to understand when the Taylorcraft strut fiasco happened that not only are punch tests NOT reliable indicators of strut weakness but X-ray, mag particle inspection, ultrasonic and visual inspection are all also pretty much useless. I proposed a simple tensile test set up that will DEFINITIVELY demonstrate if a strut is serviceable, but NIH (not invented here) syndrome seems to be well entrenched in government. The test rig is simple, reliable and performs a proof test on the strut that PROVES that it is NOT going to fail from defined flight loads. The test can also be performed by any idiot who can pull a strut off of a plane without destroying the plane.

Hank

[Scott]

Here's another link:

https://www.tsb.gc.ca/eng/rapports-reports/aviation/2019/a19c0026/a19c0026.html

frankly, with the low cost availability of usb lipstick cameras, and my experience inspecting my own struts prior to sending them for sealing, I think there's a viable option to require internal inspection via " borascope" type inspection. $25 for a sub camera, and a 1/4" hole will reveal internal strut problems with no guesswork. Kiss

[PA1195]

Even simpler...blow air through, cover any exit with a cloth, and check for corrosion particles. If found go further. Doing that to my old PA-11 struts created a cloud of rust...fresh from a previous year's punch test pattern. About 10% of the airplane's value in 2002 for new struts and forks. The plane had been on floats and skis previously.

Gary