It is highly likely that a Japanese F-35A stealth fighter jet that crashed into the Pacific Ocean did so because the pilot lost "spatial awareness", officials said.
The Lockheed Martin aircraft disappeared from radar screens during an exercise on 9 April.
Some debris and the remains of the 41-year-old pilot have been discovered.
Officials said F-35A flights, which had been halted, will resume after additional training.
This was the first reported crash involving an F-35A, according to Japan's Air Self Defense Force (JASDF).
What did investigators conclude?
The plane, which was less than a year old, crashed 28 minutes after taking off from Misawa air base in Aomori prefecture.
The aircraft came down at a speed of about 1,100km/h (683mph), officials believe.
The pilot gave no indication he was in trouble and there is no evidence he tried to eject his seat. He had only 60 flying hours in the F-35A.
The JASDF said in a press release: "It seems highly likely that the pilot was suffering from vertigo and was unaware of his condition."
It said it was unlikely the crash was caused by "technical problems with the aircraft".
Defence Minister Takeshi Iwaya told a briefing the spatial awareness issue could "affect any pilot regardless of their experience".