The US Air Force has had to ground dozens of F-22 fighter jets for the second time this year after concerns a pilot suffered a lack of oxygen in the cockpit, officers said Monday.
Commanders at a base in Virginia and in Alaska ordered a "pause" in flights for the world's most expensive and advanced fighter aircraft as a safety precaution, an Air Force spokesman said.
The decision came after an incident last week in which a pilot at Joint Base Langley-Eustis in Virginia suffered "hypoxia-like" symptoms in mid-flight, Lieutenant-Colonel Richard Johnson told AFP.
The announcement came only a month after the Air Force grounded the entire Raptor fleet from May through mid-September -- an extraordinary step -- to allow engineers to check for possible problems with the plane's oxygen supply.
Analysts say the precise source of the problem remains a mystery despite elaborate tests and safety measures.
