Are cracks on wings common amonst aircraft?
I ask as yesterday i was onboard a 757-300 and half way through the flight noticed a pretty big crack on one part of the wing. At first I thought it was a dirty water mark, but looking closer i noticed they'd patched up some other areas near to it.
So what causes cracks such as this and does it affect the performance of the wing? I'm guessing its not a critical part of the wing hence it can fly fine with it?
Any input would be greatly appreciated