Blown Lap Joints and Other Points of Fatigue

George's Point of View

The older 737's which ruptured their five-foot tops (at the lap joints) are just a drop in the proverbial bucket. Or, if you will, the canary in the cave. Because they are a sign of what is to come, if Boeing, and in fact ALL plane makers, don't step up the inspection guidelines for metal fatigue in 15 year old planes. The FAA is mandating initial and repetitive electromagnetic inspections "to detect cracking in a specific part of the aircraft that cannot be spotted with visual inspection.” The FAA Emergency Airworthiness Directive pdf can be found here.
Sure, since the fuselage crack on the Southwest 737 on April 1, older model 737's have demonstrated a propensity toward metal fatigue. On that particular plane, in March, eight instances were found of cracking in the frame and six cracked stringer clips which hold the skin. To be sure, Southwest did the right thing by grounding its 80 737s and checking them all because it turned out that five of those inspected had cracks in the same location. Those 18-inch roof sections are being repaired according to the recommendations of Boeing and the NTSB with a large aluminum patch

But what about 15 year old 757s? They should put all the older planes of comparable cycles—let's not limit this to Boeing!— What about 15 year old Airbuses? —under scrutiny for metal fatigue. Are they not just as likely to blow as a 737?

Originally posted by George Hatcher on Friday, April 8th, 2011 at 9:57 pm