Hawaii’s F-22 Raptor fighters are flying again after being grounded briefly last week in conjunction with a stand-down on the East Coast after a pilot there encountered oxygen-related problems, officials said.

"We did the same thing just as a precautionary-type thing, but we’re back up in the air flying today (Monday)," said Lt. Col. Chuck Anthony, a Hawaii National Guard spokesman.

It was the second such grounding in five months.

Anthony said his understanding is that the Hawaii Raptors were grounded for a "couple days" starting late last week. The Hawaii Air National Guard flies and maintains the stealth fighters with the active-duty Air Force.

Hawaii has received 14 F-22s, Anthony said.

The new set of concerns arose after the Air Force’s entire fleet of Raptors had its wings clipped from May 3 to about Sept. 21 as a safety precaution.

F-22 pilots elsewhere reported "hypoxia-like symptoms" — meaning not getting enough oxygen — prompting the fleet grounding. The Air Force has fielded 170 of the jets.

Anthony reiterated Monday that none of the Hawaii-based pilots has ever had the problem.

Air Force Times said one of the fighter pilots at Joint Base Langley-Eustis in Virginia appeared to have had an oxygen-related problem leading up to the East Coast grounding on Friday.

The Associated Press, meanwhile, reported that Raptors at Joint Base Elmendorf-Richardson in Alaska were also back flying Monday after they, too, had been grounded for two days.

All 20 Raptors slated for Hawaii were expected to arrive by the end of the year, but the May grounding threw off that schedule.

The Hawaii Air National Guard had seven Raptors at Joint Base Pearl Harbor-Hickam when the May grounding took effect. Two more of the planes were on the mainland for depot maintenance. Those two jets and five others have arrived at Hickam since the stand-down was lifted late last month, Anthony said.

Anthony said two more F-22s should fly to Hawaii by the end of the year. Montana Air National Guard F-15 fighters were brought in to "cover down" on the air defense mission for the state until sufficient numbers of Raptors arrived.

Anthony said the Montana unit will continue to fulfill the air defense mission until early next year, when the Raptors will assume the duty.

The May stand-down was ordered after 12 incidents of hypoxia-like symptoms were reported by pilots, the Air Force said. The incidents occurred over three years, starting in April 2008.

Secretary of the Air Force Michael Donley and Chief of Staff Gen. Norton Schwartz approved a plan for the stealth fighters to return to flight last month without detailing exactly what went wrong with the costly planes or what was done to fix the problem.

"We now have enough insight from recent studies and investigations that a return to flight is prudent and appropriate," Schwartz said at the time.

The Air Force also said the entire fleet would undergo an "extensive inspection of the life support systems before returning to flight." Pilots would use unspecified "additional protective equipment" and undergo base-line physiological tests.

Air Force Times said carbon filters were added to pilots’ oxygen supplies.

The F-22 is the most expensive fighter ever built. In April 2009 the Pentagon announced that F-22 production would end at 187 aircraft. The estimated cost of the program is $77 billion.

The Raptor, which entered service in 2005, has been deployed from bases outside Hawaii to Guam and Asia but has never flown in combat.