An antenna-like part weighing 1.4 kg fell from a F-15 fighter jet stationed at the U.S. Air Force’s Kadena Air Base in Okinawa during a flight in late February, a Japanese government source said Tuesday.

The U.S. military did not notify Japanese officials until Monday about the incident, which occurred on the morning of Feb. 27, the source said. It is not known where the part fell in Okinawa.

The part, measuring about 38 cm in length and about 15 cm in width, was found missing after the fighter jet returned to the base, according to the source.

The mishap, the latest in a series of similar incidents in recent months, could add to growing safety concerns among the residents of Okinawa, home to the bulk of U.S. military facilities in Japan.

In December, a window fell from a CH-53E large transport helicopter onto the playground of an elementary school adjacent to U.S. Marine Corps Air Station Futenma.

And last month a part from a U.S. military Osprey transport aircraft was found drifting near an islet in Okinawa. In Aomori Prefecture, local fishermen were forced to stop fishing after an F-16 fighter jet stationed at the U.S. Misawa Air Base dumped two fuel tanks in a lake due to an engine fire.