Anyone flying the world’s most advanced jet fighter must be willing to shoulder a high level of risk. We worry the F-22 Raptor is too risky.

For years now, service personnel have complained privately that this very expensive war-bird is unsafe. On May 6, two Air National Guard pilots made their concerns public on “60 Minutes.” They had taken the highly unusual step of refusing to fly the Raptor, jeopardizing their military careers.

This much we know: The single-seat, two-engine aircraft, made by Lockheed Martin, has a mysterious flaw that can deprive its human operators of breathable air during flight. The result is that pilots can become lightheaded and disoriented. The hypoxia-like symptoms have led to a series of close calls and, according to a lawsuit filed by a pilot’s widow, at least one death.

The Air Force acknowledges the existence of a problem. A year ago, it grounded the F-22 for four months to investigate. Despite failing to find what it termed the “root cause,” the Air Force cleared the planes for flight.

Michael Donley, secretary of the Air Force, told the Chicago Tribune editorial board that “mitigating measures” had been introduced to improve pilot safety. Yet it’s unclear whether those measures have worked. Critics say a charcoal breathing filter hasn’t performed as intended and is being withdrawn.

The Air Force has added sensors that measure the atmosphere inside the cockpits and monitor the condition of pilots during airborne maneuvers. The data are under review, and more are being gathered to pinpoint the flaw, Donley told us. A proposal to add a backup oxygen system also is under review.

Since their grounding came to an end in September, the planes have logged thousands of flight hours. Incidents of suspected hypoxia have occurred only rarely, the Air Force secretary said. “The return to flight, I think, is successful.”

Others are not so sure. We applaud Maj. Jeremy Gordon and Capt. Joshua Wilson, who appeared on “60 Minutes” to alert the public about F-22 safety issues. The pilots acted under a law protecting military whistle-blowers who report their suspicions to Congress. U.S. Rep. Adam Kinzinger, also an Air National Guard pilot, said Gordon and Wilson had a duty to speak up when they concluded that safety was being compromised. The Illinois Republican stood by as a witness during their TV interview in an effort to shield them from possible retaliation.

The Air Force needs to address the F-22’s unresolved oxygen issues by putting the safety of its pilots at the forefront.

As is, the nation’s 187 operational F-22s are not used in combat. The plane is designed to defeat advanced jets that rival powers have not yet developed, let alone deployed. It is being flown on training missions, which are important for deterrence, but less urgent than combat operations.

The Air Force should scale back the tempo of its Raptor flights and allow pilots concerned about their safety to withdraw from flying the planes without penalty. The process of collecting data should continue with volunteer pilots until the F-22 can be declared airworthy without the shadow of doubt now upon it.

America has invested tens of billions of dollars developing this jet, and in most respects it performs exceptionally well. The Raptor combines stealth, speed and agility with cutting-edge technology that gives its pilots amazing awareness of targets and threats. “It is still the world’s finest fighter,” Donley declared in his meeting with us.

No argument here. The Air Force needs to ensure, however, that the F-22 is the safest fighter it can be as well.