UPDATE: Maintenance error likely cause of Alaska Air 737 engine incident

An Alaska Airlines flight bound for San Diego returned to Sea-Tac International Airport shortly after it left Monday morning after reports of an “unusual vibration,” the airline said.

Part of the cowling, the metal paneling covering the engine, detached from the plane upon landing, according to a statement from Alaska Airlines. The crew aboard the Boeing 737-900ER reported an unusual vibration on the left side of the plane during departure, the statement said.

The plane is no longer in service as the airline’s safety team investigates the cause.

The two pilots on the flight have over 32 years of combined flying experience, the airline said.

There were 176 passengers and six crew members on the flight, according to the statement. No injuries were reported.

Guests were rebooked on another flight bound for San Diego, the company said.

The pilots and flight attendants handled the incident with “tremendous professionalism and care,” the airline said in the statement. “We also greatly appreciated the patience of our guests during this event.”