Cracking Up at 65% of rated cycles

Boeing Says It Didn’t Expect Cracks in 737s So Soon - NYTimes.com: "A Boeing engineer said Tuesday that the company had projected a longer lifespan for the skin and the supporting joints of its older 737 jetliners and was surprised that serious cracks developed on one Southwest Airlines plane last Friday.

Paul Richter, a chief engineer for the older Boeing 737 models, said the plane maker had expected the parts to last 60,000 cycles of takeoffs and landings before cracks might form, while the jet that developed the hole on Friday had only 39,000 cycles. Southwest had done nothing wrong in maintaining the plane, Mr. Richter said."