The Boeing 777 of Japan Airlines, registered as JA8978 was operating flight JL904 from Okinawa-Naha Airport (OKA) to Tokyo-Haneda Airport (HND), on December 4, 2020.

Six minutes after takeoff, at an altitude of about 5,500 meters (18,000 feet), about 74 kilometers (45 miles) north of Naha Airport, a loud explosion was heard coming from engine #1 (a Pratt and Whitney PW4074). Pilots declared an emergency and turned back to Naha. No injuries were reported among the 11 crew members and 178 passengers on board.

The initial inspection revealed that the engine cover appeared to have come off during the flight. Two fan blades were severed from the root and the case surrounding them was also damaged, the Japanese Ministry of Land, Infrastructure, Transport, and Tourism said. Japan Transport Safety Board evaluated the mishap as a “serious incident” that could lead to a major accident and launched an investigation.