A steel bolt assembly may have come off a Maritime Self-Defense Force helicopter during a training flight Tuesday, the MSDF said.
The bolt and accompanying washers, used to secure submarine search equipment on the chopper, were discovered to be missing following the drill, the MSDF said.
No damage has been reported on the ground, according to the MSDF's Maizuru district headquarters in Kyoto Prefecture.
The SH-60K antisubmarine helicopter took off from the Maizuru airfield shortly after 11 a.m. Tuesday and landed at the Tateyama airstrip in Chiba Prefecture near Tokyo in the afternoon before returning to Maizuru.
The roughly 3-centimeter-long and 1-centimeter-wide bolt weighing about 10 grams, and the washers weighing around 0.1 to 0.4 grams each, were found to be missing at about 6:30 p.m., following the five-hour flight.
No abnormality was detected during the inspection conducted before the drill and the flight was unaffected. The aircraft flew at an elevation of 750 to 3,300 meters over cities that included Kyoto, Otsu, Nagoya and Tsu, according to the MSDF.