The Air Force says its F-22 fighter jet is heading back to normal operations following the discovery of the cause of altitude sickness among pilots.

FOX News Radio's Steve Taylor has the story from Washington as part of our ongoing series on national security:

Securing America.

After five pilots complained of dizziness and showed other symptoms of hypoxia, an oxygen shortage in the brain, the Air Force put altitude limits on F-22 flights. Now an investigation of the pilot breathing systems finds the air was all right.

(Little) "Oxygen contamination was ruled out."

But, Pentagon spokesman George Little says, pilots weren't getting enough oxygen. So a valve is being replaced and a filter removed. If that works, Little adds...

(Little) "The gradual lifting of restrictions will enable the Air Force to resume normal F-22 operations over time."

For now, a squadron of F-22's will fly the Pacific to test the breathing systems.

In Washington, Steve Taylor, FOX News Radio.