The pilot of an F-35A fighter jet that crashed into the sea off northern Japan on Tuesday apparently had no time to eject before the crash.
Air Self-Defense Force officials say the F-35A stealth fighter is equipped with an emergency system that ejects pilots from the cockpit and allows them to parachute.
But the officials say they received no signals that the system was activated during the incident.
An investigation so far has found that the pilot radioed before his plane went down, saying that he was cancelling the training mission.
SDF officials say the pilot may have had no time to follow evacuation procedures after he confirmed signs of some trouble.
The pilot in his 40s remains unaccounted for. SDF aircraft and vessels have been continuing their round-the-clock search.