Qantas Airways Ltd. and Southwest Airlines Co. have stepped up checks for structural cracks on Boeing 737 NGs after discovering problems Boeing has grounded up to 50 planes globally over cracks, Agence France Presse news agency reported on Thursday. Boeing was not immediately available for comment. Qantas Airways Ltd. and Southwest Airlines Co. have stepped up checks for structural cracks on Boeing 737 NGs after discovering problems with planes that did not require urgent inspections, Reuters reported, citing airline sources.