The United States Air Force has grounded its entire fleet of F-22 fighters, the most sophisticated combat aircraft in the world, after problems emerged with the plane's oxygen supply.
The Air Force is probing possible breakdowns in the oxygen supply system for the radar-evading Raptors after several pilots reported problems, according to the journal Flight Global.
The Air Force has more than 160 of the aircraft in its fleet.
The planes have not been used in the NATO-led air campaign in Libya or in the wars in Afghanistan and Iraq.
