spar cracks
Volume, i may have mis-understood the context of your post but to say that "any wing spars on ageing a/c have cracks" seems to be a very bold statement. I work on a/c that are classed as ageing a/c and thus subject to CPCP inspections and checks and yet I would like to think that if a spar crack was found on any of our a/c then it would be grounded until repair action carried out and also a fleet-wide check carried out. I may have mis-interpreted your post but I couldn't help feeling that this sort of thing is a normal occurrence. My understanding of the principle of "failsafe" structure is that, yes a crack could develop and be missed on an initial inspection and that if the crack spread to the point that the section in question failed, then the remaining structure is designed to bear the loads under all flt/gnd conditions until the next inspection where the defect would be so obvious it should be picked up. I would be interested to know how often you come across cracks that are "large and visible during routine inspection" and in what area's of the structure. I have only experience on one type and certainly don't come across defects as severe as this example very often at all.
I apologise in advance if I have mis-understood and did not intend any offence, but your comments surprised me somewhat, i look forward to a reply
Eng