When an aircraft engine is overhauled, lots of parts have to undergo non-destructive testing. As the two guys who have been doing it at our shop are getting progressively busier with other tasks, I was recently sent to school, as a result of which I am now a Level 2 NDT inspector in magnetic particle testing (aka Magnaflux). A fantastically interesting course. The entire field of NDT is somewhat like flying, meditation or martial arts: no matter how many books you have read, there is no substitute for person-to-person instruction, and there are many steps on that path. At first, you become a trainee and need to accumulate 50-200 hours (depending on method and industry) under the supervision of a qualified inspector and take a week-long course at the training centre, then pass a test and become Level 1, who can perform examinations in accordance with written procedures and can record the indications but cannot interpret them. Then you accumulate several hundred more hours, take another course, pass another test and become a Level 2 inspector, who can also set up and check the NDT equipment, interpret the indications and sign a protocol. Or you can take an integrated course and become a Level 2 from scratch (same hours, same two courses, but just one test). If you are serious about this career, after four years of full-time work (or one year + a science/engineering degree) you can go for a Level 3, who can also create the written procedures for the Level 1/2 folks and take general responsibility for the whole outfit (possibly more than one). Some Level 3 specialists who are qualified in multiple methods and have teaching experience, scientific publications or similar merits become members of National Aerospace NDT Board. Finally, these boards across Europe are members of the European Forum for NANDTB under the aegis of the European Federation for NDT. The entire discipline is highly standardised and internationally harmonised, yet a very significant part of the process depends on inspector’s skill, understanding and eyesight. In particular, it requires a visual acuity test every year and a color vision test every 5 years (everyone understands that the latter one is superfluous, yet the standard says so).
If anyone is curious about the inner workings of NDT, I’ll be happy to share what I know. And for those who actually need NDT done on their components, our shop is licensed to provide such services to outside customers.
Well done on your Level 2 NDT Inspector!
Though I vaguely thought I knew some distant thing about NDT, your short explanation and the required training and qualifications demonstrate the complexity of the subject, thanks for sharing.
PS
I’ve had an engine failure following a connecting rod failure on a O-320 in 2008. The outcome was positive, but I sold the wreck including the exploded engine.
And always wondered: the broken conrod threw some pieces of the case away, and poking thru one of the holes I took a couple of pictures, but unfortunately had other things on my mind rather than to pursue my investigations and take better shots… so I still don’t know what part really failed, the connecting rod, the connecting cap, or one of the 2 retainer bolts.
The engine was quite old and had been overhauled a couple of times, I therefore suspect inter granular fatigue, eventual corrosion as well, as the source. AFAIK conrods are NDT inspected prior to being reused, but would such a fatigue be detected in its early stage?
Often when an engine ‘throws a rod’ the root cause is a fault in the bearing shell, sometimes that the shell rotates, misaligning the oil supply hole which shuts off the oil supply. Another common cause is loss of oil pressure from any source. The root cause is less often fatigue in the connecting rod itself, although it could be.
Dan wrote:
conrods are NDT inspected prior to being reused, but would such a fatigue be detected in its early stage?
Actual fatigue cracks can be detected by NDT, and they always start at the surface. Fatigue at the microscopic level is much more difficult, but sometimes there are indirect methods. For example, Czech inline piston engines (Walter and LOM) have connecting rods of aluminium alloy. Once overheated in operation, they succumb to fatigue much faster, but it can be recognised by the loss of hardness. So, in the course of overhaul or other major service we always measure rod hardness at two points near the little end, and if it’s below 120 HB (or 69 HRB), the rod needs to be replaced.
Thanks gentlemen, all very interesting stuff 🧐
