PSA: Found a crack in a 737 bulkhead that looked like a scratch at first

Was doing a routine C-check on a 2008 737-700 last Tuesday and noticed this faint line near the aft pressure bulkhead. Got the NDT guys in and it turned out to be a growing fatigue crack that started from a previous repair about 2,000 cycles ago. Anyone else run into hidden cracks that looked way too subtle on first look?

2 comments

2 Comments

west.henry1mo ago

Hold up. I see it different. A scratch that turns into a crack after 2,000 cycles sounds like somebody skipped a step during the last repair. Fatigue cracks don't just magically start from nothing. They grow from bad work. I've seen it on pressure washer frames. A weld that looked fine at 500 hours turned into a failure at 800. The NDT guys found the problem in your case, which is good. But the real issue is why that repair job didn't catch it in the first place.

bennett.noah1mo ago

You're right, I used to think fatigue cracks were mostly a material defect thing. But seeing it spelled out like this with the repair timeline makes more sense now. It's easy to blame the metal or the cycles, but the real story is usually bad prep work or a missed step in the last repair. NDT catching it is good, but they shouldn't have to find something that should have been fixed already. I'm going to look at past repairs differently now, thanks for laying it out that way.