Overheard a guy at the parts counter say most cracks start in the first 50 hours of flight time...

I was standing at the parts counter last Thursday waiting for some cotter pins and I heard this older mechanic telling a younger guy that he checks for fatigue cracks right after the 50 hour mark on any new-to-him plane. It got me thinking about my own inspection habits. I usually just eyeball things during my annuals and figure if it flew in fine it's probably okay. But this dude pointed out that early stress cycles are when metal really lets go, especially around rivet lines on older Cessnas. Now I'm gonna add a more focused crack check at that 50 hour window on my next project plane. Anyone else ever heard a specific time frame like that for when cracks pop up?

2 comments

2 Comments

ryanprice25d ago

Did you hear about that study AOPA did a few years back on crack formation in general aviation planes? I remember reading it and they basically said the same thing - most of the serious structural cracks they found showed up within the first 50 to 100 hours after a plane changed hands or got a major repair. Something about the metal settling into its new stress patterns or whatever. That old timer at the counter probably learned that from experience, not a book. Makes sense though if you think about it, the first few flights after a change are when everything gets tested hardest. I started borrowing a borescope from my buddy after hearing that same advice and now I hit every rivet line and spar carrythrough at 50 hours on any plane I buy.

jamiesingh25d ago

Yeah man, @ryanprice that study is spot on. I had a buddy who bought a Cherokee six, and at maybe 60 hours in, we found a hairline crack along the spar carrythrough near the flap bracket. It was tiny, but it was there. I've seen the same thing with a 172 that had a new engine mount put in - at around 80 hours, a crack showed up right where the mount bolts to the firewall. So now I do what you described with the borescope at 50 and 100 hours on every plane I bring home. It's wild how much stuff pops up right when you think everything is settled in. The old timers really did figure it out just by keeping their eyes open.