The search continues for a Japanese Air Self-Defense Force F-35A that went down off the coast of Honshu in northeast Japan last Tuesday. The pilot, Maj. Akinori Hosomi, remains missing.

Days after the Joint Strike fighter went missing on Japanese radar, bits of wreckage were found in the Pacific, confirming reports the aircraft crashed, but offering little evidence as to why. Now, a report published by the Japanese newspaper Mainichi Shimbun claims that Japan’s small fleet of F-35s experienced a number of issues—resulting in no fewer than seven emergency landings by five aircraft in recent months.

The country received a total of 13 F-35s thus far, with five experiencing in-flight emergencies that forced immediate landings. Despite reports painting this as an American failure, four of these five jets underwent final assembly not in American-based Lockheed Martin production facilities, but rather on Japanese soil by Mitsubishi Heavy Industries, Ltd. The F-35A that went down last Tuesday was also among the first jets assembled by Mitsubishi.

Currently, all of Japan’s F-35s are grounded.