TOKYO >> A group of U.S. F-22 stealth fighters arrived in Japan today in what the Air Force hopes will be a step toward proving that its prized aircraft are safe after a mysterious oxygen problem that was making pilots sick.

The F-22s arrived at Kadena Air Base from the United States and were expected to remain on the base, on Japan’s southern island of Okinawa, for several months. Japanese media said eight of the aircraft had arrived by Saturday evening. Another four were expected to arrive later. Base officials were not immediately available for comment. 

The F-22, manufactured by Lockheed Martin Corp., is the Air Force’s most advanced stealth fighter. It was built to evade radar and is capable of flying at faster-than-sound speeds without using afterburners. 

But the fleet has been under tight flight restrictions since mid-May because pilots were reporting dizziness and other symptoms of hypoxia.

The Air Force says the deployment to Japan is a first step toward returning to normal. Before they left, the Air Force said the aircraft would take a special route to ensure they had possible landing sites along the way and would fly at lower altitudes, where the cockpit oxygen issue is less problematic.

On Tuesday, U.S. Defense Secretary Leon Panetta approved a plan to send the fighters to Japan and begin lifting the restrictions because he said the Air Force has identified the cause of the problem and has taken measures to fix it. 

The Air Force believes the troubles stemmed from a valve in the pilots’ pressure vest that caused it to inflate and remain inflated, triggering breathing problems. The Air Force is replacing the valve and increasing the volume of air flowing to the pilots by removing a filter that was installed to check for contaminants in the system.

The flights to Japan were to be flown at low altitude so that the vests would not have to be used.