[Flieger]

Originally Posted by Jeff Higgins

Well, there is really no such thing as a "cracked wing". There may be cracked wing components, and that's what Airbus is faced with.

In retrospect, I think I was too hard on you, Fliegler. Sorry about that, I think I misunderstood your point.

Yes, by all means, parts crack. Every single structural part has a predicted mean time to failure. We more or less "know" when it's going to happen. What we decidedly do not do, however, is allow any given part's service life to extend beyond even any initial cracking, and continue to fly it while proclaiming "yeah, we knew it would do that".

We endeavor to replace or repair cracked parts as soon as possible, especially those that have cracked unexpectedly. It becomes very difficult, if not impossible, to predict the rate of crack propagation when we have well and truly missed on its mean time to failure anyway. In these cases, inspection intervals are severely compressed, and we monitor the situation very closely.

Inspections on parts approaching a certain percentage of their mean time to failure become more vigorous as well. Parts are replaced at some percentage of their predicted lifespan (depending on application and relation to safety of flight). These parts get pretty thoroughly analyzed in an effort to validate our predictions.

So, yes, you are technically quite correct - airplanes do have a designed-in, finite lifespan. Just not at an "entire airplane" level, which is kind of how I read your post. (I don't think that's what you meant.) It's really the individual parts that make them up that do. There are, however, very few we cannot replace, even in the field. So, technically, airframes really do not have a "designed lifetime", but parts of them do.

OK, now you are making sense. Yes, by an aircraft lifetime I meant lifetime until something big enough starts cracking such that it is not worth repairing.

By the way, "Are you an Engineer?" was an authentic question. I knew you were with Boeing, but did not know if you were a skilled worker in assembly or an Engineer or both...