An Air Self-Defense Force F-15 fighter jet made an emergency landing at the U.S. Air Force's Kadena Air Base in Okinawa Prefecture on Monday morning after a hydraulic system failure was detected, defense officials said. The pilot was not injured in the incident, which the officials said the ASDF was investigating. The fighter jet, assigned to the ASDF's Naha Air Base, took off from Naha Airport at around 8:20 a.m. Monday and was flying in airspace reserved for training northwest of the airport. Officials said the fighter jet detected a malfunction about 10 minutes after takeoff. Naha Air Base's F-15 fighter jets made emergency landings at Kadena Air Base during training under similar circumstances in January and May this year.