More details regarding the April 9 loss of a Japan Air Self-Defense Force F-35A flying from Misawa air base have emerged in recent days. A major search continues to locate the missing pilot and the aircraft.

The pilot has been identified by the JASDF as Major Akinori Hosomi, 41, an experienced pilot with around 3,200 flying hours, of which 60 were in the F-35A. According to press briefings by the JASDF and Japan’s defense minister Takeshi Iwaya, the aircraft was one of four that launched for an evening air combat training sortie. Hosomi called for the formation to end the training portion of the sortie before his aircraft disappeared from radar. No further communication was received. The F-35 is equipped with a system that sends a distress signal if the ejection seat is fired but, according to a report by The Mainichi newspaper, the JASDF confirmed that no such signal was received.

In response to the missing aircraft, Japanese maritime forces launched a major surface search, with support from the guided-missile destroyer USS Stethem from the U.S. Navy’s Seventh Fleet. Boeing P-8A Poseidons joined the aerial search alongside various Japanese aircraft. Some wreckage—reportedly from the F-35A’s twin tails—was found and recovered. U.S. Forces Japan (USFJ) also revealed that the Lockheed Martin U-2R had been used in the search, presumably aircraft from the 5th Reconnaissance Squadron, which are normally based at Osan, South Korea, but also often operate from Kadena air base on Okinawa. U.S. officials also denied rumors that Boeing B-52 bombers participated in the search.

Now an undersea search has been launched to locate the F-35 and its pilot, which are thought to have crashed into the ocean in an area where the depth is around 1,500 meters (4,920 feet). The submarine rescue vessel JS Chiyoda has been dispatched to the area. It is equipped with seabed-scanning sonar and deep-sea submersibles with cameras.

While, naturally, the first concern is to locate the pilot, there is a pressing need to recover the aircraft and its flight data recorder to help establish the reason for the loss. The JASDF has grounded its 12 F-35As, and other operators have considerable interest in establishing the causes. There is also a significant security angle, as China and Russia would both have a clear interest in finding the wreckage. Minister Iwaya told Japanese media that no unusual activity had been detected in the crash area, but that it is being closely monitored.

A factor that may have no bearing on the investigation, but will be taken into account, are two previous incidents to befall the aircraft in question. State Minister of Defense Kenji Harada told a lower house committee on April 11 that it had aborted flights in June 2017 and August 2018, but in both instances, the causes had been traced and the defective parts replaced.