WASHINGTON (AP) — An Air Force advisory panel says it still can't explain what caused blackouts and dizziness among pilots flying its supersonic F-22 Raptor.

Officials told a Pentagon press conference Thursday that the stealth fighter is safe and continues to fly in the continental United States, with pilots using special sensors, filters and other safety steps to mitigate problems with the plane's on-board oxygen system.

The Air Force says it's putting into place a number of safety recommendations made in the seven-month study.

Retired Air Force Gen. Gregory Martin, who headed the study panel, said officials will continue to study the problem until they find its cause.

The Air Force's entire fleet of those fighters, which are made by Lockheed Martin Corp., was grounded for four months last year until mid-September after pilots complained of lack of oxygen.