From Investing.com:

An Alaska Airlines Boeing 737 MAX 9 suffered a scare after a panel tore off the left side of the aircraft, forcing the pilot to turn back and make an emergency landing. The panel, known as a plug, is installed on some MAX 9s in place of an additional emergency exit. Of the 200-plus 737 MAX 9 planes Boeing has delivered, 171 have this panel in place of a door. The installation is a two-tier process involving both manufacturing at Spirit’s giant fuselage plant in Wichita, Kansas, and a Boeing factory outside Seattle, the sources said.



Read more: Explainer-What is the panel that blew off a Boeing plane in mid-air? By Reuters