Boeing has revealed it is reworking 50 undelivered 737 MAX jets after mis-drilled holes were found in some fuselages. Spirit AeroSystems, which has faced previous quality issues impacting 737s, supplied the fuselages. The issue could delay some Boeing deliveries in the near future while allowing existing 737s to keep flying. Boeing says finalizing rework instructions and determining timelines to address the issues. Delays will allow thorough inspections and fixes. The discovery comes after increased regulatory scrutiny of Boeing's production practices following recent incidents.