Shares of Boeing and parts supplier Spirit Aerosystems tanked Monday after the Federal Aviation regulators grounded certain Boeing 737 MAX 9 jets for further inspection after a piece of fuselage tore off the left side of an Alaska Airlines-operated aircraft on Friday, causing the airliner to make an emergency landing after the cabin depressurized. Shares of Alaska Airlines also fell. 

The aircraft was approaching 16,000 feet of altitude when it experienced rapid depressurization after a panel that serves as a plug for an emergency exit door used on some variations of the Boeing 737 MAX 9 was torn off. The pilot immediately signaled the plane would have to land, and it safely returned to Portland, Oregon, with all 171 passengers and six crew members aboard.

No serious injuries were reported in the incident, and nobody was sitting in the seats adjacent to where the door plug blew out, according to the airline. Parts of the seat next to the fuselage, including the headrest, were missing.

Dow member Boeing traded at a one-month low as tracked by Dow Jones Market Data Group. 

FOX Business' Eric Revell contributed to this report.