Japan's air force said "spatial disorientation" likely caused one of its pilots to fly his F-35 stealth fighter into the Pacific Ocean in April, hitting the water at more than 1,100 kilometers per hour.
The Lockheed Martin Corp jet disappeared from radar screens during an exercise with three other F-35s over the ocean off northwest Japan on April 9. The 41-year-old pilot was killed.
"We believe it highly likely the pilot was suffering from vertigo or spatial disorientation and wasn't aware of his condition," Defense Minister Takeshi Iwaya told a briefing yesterday.
"It can affect any pilot regardless of their experience."
By dismissing mechanical or software problems as a cause for the advanced fighter's crash, Japan's assessment is likely to come as a relief to other countries that operate or plan to introduce the US-built jet, including Britain and Australia. Iwaya said Japan would increase vertigo training for its pilots, check its remaining F-35s and meet residents living near the base from which they operate, in Misawa, Aomori prefecture, before restarting flights.
The air force has yet to recover any intact data from the US$126 million (HK$982.8 million) aircraft's flight data recorder to back its assessment, which is based on data and communication received by ground controllers and interviews with other pilots.
Japan says it eventually wants to field a force of about 150 F-35s - built by Lockheed Martin Aeronautics - making it the biggest overseas purchaser of the single-seat fighter, as it tries to keep ahead of China's advances in military technology.