SEOUL, South Korea (AP) — A Korean Air flight to Taiwan was forced to return to Incheon airport west of Seoul after a sudden depressurization on the plane, a Boeing 737 Max 8.

The transport ministry said 19 of the 133 people aboard the flight Saturday were sent to hospitals, but none suffered serious injuries.

An airline spokesperson and the ministry said the cause of the problem was under investigation.

The aircraft was grounded and the ministry ordered South Korea’s 11 airlines to examine pressurization systems in all their 400 aircraft.

Separately, Malaysia Airlines said one of its flights en route to Bangkok on Monday made a U-turn back to Kuala Lumpur after the Airbus A-330 experienced a “pressurization issue.”