The Air Force has grounded 116 C-130Hs, more than 20 percent of the fleet, after it was determined that inscriptions scratched in the propellers documenting inspections for cracks actually caused cracks. “The process used to engrave serial numbers on the propellers likely contributed to cracks that are being found on the C-130Hs,” Maj. Beau Downey, an Air Force spokesperson, told Defense One. “That process, which involved an electric arc pen to incise digits into the surface of the metal, was stopped about six months ago and will not be used going forward.”
Really? Really? It’s not like advice on the matter has not been around for YEARS!
ACS 43-13 8-93. METAL PROPELLERS AND BLADES.
These propellers and blades are generally susceptible to fatigue failure resulting from the concentration of stresses at the bottoms of sharp nicks, cuts, and scratches.
Kinda wonder as a retired A&P who was minding the store on maintenance at USAF when they were doing this. Even a brand spanking new A&P knows better. Bizarre.
My guess is O3 Captain Smith had just enough brass and just enough ignorance to command E2 Jones to do it, and E2 Jones followed orders shaking his head.
Every time my mother (A WWII Veteran) tried to number her children, she’d lose track somewhere between #2 & #5. That always caused the next child to crack. Finally, after the youngest was sent to the principal for disrupting the class with prolonged laughter, she gave us names.
She solved the cracking problem, and gave us our props.
Children are taught early and often that the appearance of hard work gets rewarded more than accomplishment. Institutions that cannot figure out how to measure actual effectiveness will quickly start measuring the ability to please the leaders. The leaders will then replicate themselves. Within a couple generations you now have a shadow of the original organization.
How many times as a pilot AC owner were we told about dangers of nicks and scratches on our props and what could happen? Every annual my prop came back smooth and clean with all the nicks and dings cleaned up. Supposedly such cleanups were to be done by a prop specialist but the shops deemed removal of such flaws of very high importance, and someone in the shop did the job because they all knew not doing it was potentially dangerous or at least very expensive down the road. Be interesting to know how much a Herky bird prop blade costs.
You know how “people these days” use the word “ironic” to mean damn near anything EXCEPT irony? This, my friends, is the definition of irony. Literally.
Wasn’t there a crash a while back where the #2 prop came off ,cut the fuselage, and then hit the #3 prop/engine.Then 3 prop came off and cut the fuselage again and caused the nose to separate?
All these comments about the ‘stoopid’ air force and how obvious it is not to stamp, nick, or scratch a prop seem to forget that when a typical GA prop is repitched, the old pitch is X’ed out and the new pitched is… wait for it… stamped into prop.
The article above doesn’t have enough detail. Were these new numbers engraved into the prop blade? The shank? The face end inside the hub? I expect a full telling of the story would show that the location and type of engraving were in a seemingly non-critical area. Except, of course, to the team of prolific commenters led by Captain Hindsight.
I’m no expert in prop stress, but I do know that in other rotating machinery, there is a right and wrong way to imprint or form the device. That’s one reason why some threaded parts have rolled threads instead of cut threads. There is also a procedure for how to imprint data into the surface of pressure vessels to avoid the stress risers caused by a simple pin punch. I would hope that someone checked into the process of electric arc engraving to see if it would cause stress risers before approving it for this application. Maybe the procedure was acceptable for certain locations, but was applied in the wrong place? The Air Force seems unwilling to provide enough detail to fully explain the issue.