The flight left Portland at 4:52 pm but returned just before 5:30 pm (local time).
The plane rose as high as 4876 metres during the flight and then began descending, according to data on the flight tracking website FlightAware.
KPTV-TV reported photos sent in by a passenger showed a large section of the aeroplane’s fuselage was missing.
The FAA did not immediately respond to an email request for information.
The Boeing 737-9 MAX rolled off the assembly line and received its certification just two months ago, according to online FAA records.
The National Transportation Safety Board said in a post on X, formerly known as Twitter, that it was investigating an event on the flight and would post updates when they are available.