An AD should be issued requiring all operators of transport-category airplanes with certain pressure-vessel structural repairs to determine if they were done properly or whether there’s hidden damage that could lead to multiple-site fatigue cracking and possible structural failure, according to the NTSB. The Safety Board’s recommendation stems from its investigation into the structural breakup of a China Airlines Boeing 747 on May 25 last year. Improper repair of a fuselage doubler allegedly led to a structural failure that brought down the 747.