From Investing.com:

Spirit AeroSystems manufactured and installed the fuselage part on a new Boeing 737 Max 9 that suffered a blowout, with Boeing also involved in the completion process. Regulators grounded most 737 MAX 9s after an Alaska Airlines plane lost a door-replacement panel during a flight. The investigation will examine whether flaws occurred during installation and manufacturing. Most airlines using the jet have chosen a looser layout based on a smaller number of seats, and do not need the surplus door. Spirit builds and sends fuselages for 737s with the special door assembly “semi-rigged,” and Boeing typically removes the non-functioning door to load interiors before completing the installation. The investigation will include structural experts to determine if design or manufacturing played a role in the incident.



Read more: Spirit Aero made blowout part but Boeing has key role -sources By Reuters