Dye Penetrant Crack detection in props

[Matthew Rogers]

With the talk about dings and nicks in propellers, do AP/IA regularly, or ever, use dye penetrant testing on a propeller? It seems to be quick, easy, and better than eyes for hairline cracks. With that said, is there anything preventing an owner from spending $50 for a set of the chemicals and doing it themselves once a year?

This kit for Aluminum would last for a long time at $35.
https://regismanufacturing.com/kwik-chek-crack-detection-spray-kit-for-aluminum-kck/

If you find anything concerning, it would be easy to mark it for the AP or give you a heads up that your prop will probably be sent to (and rejected by) the prop shop.

 

[Bell206]

do AP/IA regularly, or ever, use dye penetrant testing on a propeller?

No, in general, but there are some very specific exceptions. Most non-destructive testing (NDT) has moved on from the visual dye check products for various reasons. The most important reason being those types of liquid dyes promote corrosion and are even outlawed in a number of uses. In addition, because NDT can require specific skills to ensure a proper result, most aviation OEMs now require a level 2 or level 3 NDT rating to perform the checks which does not include 98% of APIAs. And finally there have been several prop failures from using the visual dye method vs the required ultraviolet dye check method as the visual dyes can't detect as effectively as the ultraviolet dyes. So no it would not be a good idea for you to check your prop.

 

[Matthew Rogers]

No, in general, but there are some very specific exceptions. Most non-destructive testing (NDT) has moved on from the visual dye check products for various reasons. The most important reason being those types of liquid dyes promote corrosion and are even outlawed in a number of uses. In addition, because NDT can require specific skills to ensure a proper result, most aviation OEMs now require a level 2 or level 3 NDT rating to perform the checks which does not include 98% of APIAs. And finally there have been several prop failures from using the visual dye method vs the required ultraviolet dye check method as the visual dyes can't detect as effectively as the ultraviolet dyes. So no it would not be a good idea for you to check your prop.

Ok, so aside from the corrosion issue (which may only be for some materials - see below), how does performing extra checks actually hurt? That is like saying "since you are not an AP/IA, why bother inspecting your own aircraft for discrepancies since you are not a trained professional". If this test is never performed by the AP/IA and you are only 30% effective at catching an invisible growing crack, that is still better than the 0% chance without the testing. What is the harm in performing the test?

UV dye penetrant kits are easily available $65 (plus a uv lamp, which I already own)
https://www.pegasusautoracing.com/productdetails.asp?RecID=5922

In addition to being approved to AMS 2644, Ardrox® 970P25E is approved by all major aerospace engine and airframe manufacturers including General Electric, Rolls Royce, McDonnell Douglas, Boeing, Pratt & Whitney and Rockwell (fracture control inspection for B-1 aircraft applications.) For the nuclear industry, these products are designed to conform to the requirements of the ASME Boiler and Pressure Vessel Code (Section V, Article 6) and AECL.

Ardrox® 970P25E is non-corrosive to most common metals. It meets the corrosion requirements of AMS 2644 for aluminum, steel and magnesium. It is compatible with titanium and nickel alloys. It may stain or soften some plastics and rubbers; where appropriate, a compatibility test is recommended.

 

[Morgan3820]

Dye penetrant has been around for decades. If it was indeed useful in the situations that you use as an example, don’t you think that it would already be in use? Maybe APs know something that you don’t.

 

[Matthew Rogers]

Dye penetrant has been around for decades. If it was indeed useful in the situations that you use as an example, don’t you think that it would already be in use? Maybe APs know something that you don’t.

Maybe, that is why I am asking. I got an answer from Bell206 that was mostly about industry certifications, which probably don’t apply to a GA mechanic, or owner.

Plenty of stuff is not performed because of outdated training (“we didn’t do it like that 30 years ago, why do it now?) or previously costly materials and tools which are now cheap and easy (Boroscopes).

I want someone to answer the question, what is the harm in looking for a crack? If you do it right and find an invisible crack, that is a win. If you do it wrong and don’t find one that is there, you are at the same place you were before the test, not any worse off as you would not be able to see it anyway. If the crack is big enough that you can see it with a magnifying glass (the only thing that AP/IAS can use apparently), you will be hard pressed to screw up the crack detection process.

 

[Jim K]

I'm not an expert on anything, but it seems that stresses in a propeller would be such that the only time there would be a detectable crack would be a microsecond before rapid unplanned disassembly. That's why it's so important to eliminate any stress risers by dressing out nicks.

But knock yourself out.

 

[biplanebob]

I have used dye penetrant to verify that something I have already found visually is indeed a crack.

 

[Silvaire]

It's NDT. Non Destructive Testing. So, do it all you want, did you think it was somehow illegal?

 

[Craig]

Dye penetrant requires a clean surface to start with. Unless you have a bare prop, you would need to strip the test area first. I used to do penetrant inspections on parts that had suspected cracks using Zyglo, when I worked the F-16 line. We've gone to strictly eddy current or ultrasound, or x-ray since those days.

 

[Bell206]

that was mostly about industry certifications, which probably don’t apply to a GA mechanic, or owner.

FYI: they do by virtue of Part 43.13(a) & (b).

how does performing extra checks actually hurt?

It can also cause future required checks to fail if not done properly to the point that the FAA issued a policy letter not to use visible dye penetrates on safety critical parts. I couldn’t get the memo to link but here is an article that gives the memo number and a summary of what it stated.
https://cessnaowner.org/faa-issues-saib-on-propeller-maintenance/

That is like saying "since you are not an AP/IA, why bother inspecting your own aircraft for discrepancies since you are not a trained professional".

Not at all. I just don’t like to see a person to fail. And you took a step in that direction. Had your question asked what you could do more in checking your prop, I would have detailed what is done in my experience like follow the OEM recommendations keeping the prop clean, dressed, and protected. Then if you have spots that are questionable, check them with a bright light and 10x glass. This is the standard next step in most maintenance procedures, instructions, and other references. If there still is a question after the 10x check, pull the prop and send it to a shop for a proper inspection. But its your plane and your call.

 

[Let'sgoflying!]

I couldn’t get the memo to link but here is an article that gives the memo number and a summary of what it stated.

 

[Bell206]

what is the harm in looking for a crack?

Here's the FAA Policy Memo as well:
https://rgl.faa.gov/Regulatory_and_...tical,parts,for,engines,,propellers,,and,apus

 

[JAWS]

Hartzell used to require NDT of their blades after the blades were dressed, as well as using a 10x to inspect the repaired area. There was enough push back that they changed the word "shall" to "recommend" the NDT portion.

Instead of NDT, why not get a 10X magnifier? Cheaper, more versatile, can start a fire if needed on a sunny day! Use it to pre-flight.

 

[Let'sgoflying!]

I looked but now cannot find, a reference from last year where all dye testing was poo-pooh'd because a subsequent, more reliable test could not be performed after the dye was applied.
The dye would disguise a defect which MPI - or maybe it was ECI - would normally be able to detect but would show a false negative after use of dye.
If anyone can find that, I need to review it.

 

[Dan Thomas]

McCauley issued an SB maybe 12 years ago demanding NDT after any prop dressing. In Canada NDT must be done by certified NDT technicians, so it would be horrifically expensive. Thankfully it was only an SB.

NDT done by an amateur can give a false sense of security since there is so much to know about that technology and it's easy to miss something. IIRC it's a 48-month course here. Serious training.

 

[Dan Thomas]

I'm not an expert on anything, but it seems that stresses in a propeller would be such that the only time there would be a detectable crack would be a microsecond before rapid unplanned disassembly. That's why it's so important to eliminate any stress risers by dressing out nicks.

But knock yourself out.

No. Cracks have often been caught visually before failure.

 

[JAWS]

If this test is never performed by the AP/IA and you are only 30% effective at catching an invisible growing crack, that is still better than the 0% chance without the testing. What is the harm in performing the test?

Any dye penetrant inspection requires that the flaw being looked for is on the surface. And that surface has to be stripped, clean and relatively smooth. The harm may come in false positives (crack found, when it isn't there) or false negatives (no crack found, when in fact there is one).

I'd rather someone spent the time and money to get better general inspections than hyper-focusing on one area. A well dressed, inspected and painted prop will do more than any dye pen test that isn't warranted. There are some props that require routine (certified) NDT inspections due to an AD or SB or AWL.

 

[JAWS]

McCauley issued an SB maybe 12 years ago demanding NDT after any prop dressing. In Canada NDT must be done by certified NDT technicians, so it would be horrifically expensive. Thankfully it was only an SB.

NDT done by an amateur can give a false sense of security since there is so much to know about that technology and it's easy to miss something. IIRC it's a 48-month course here. Serious training.

I used to be Appendix K certified for fluorescent on a few specific tasks. Annual training and performance testing and keeping a logbook of each inspection. Went by the wayside after NDT AMO's started charging more to keep up on my certification than to perform the actual inspections.