Air Force generals will go before a congressional subcommittee today to testify about breathing problems that have affected F-22 Raptor pilots and possibly contributed to two fatal crashes.

After the hearing before the House panel on tactical air and land forces, the Air Force will release a report prepared by its own Scientific Advisory Board, which was convened to investigate repeated breathing difficulties and disorientation among F-22 pilots in flight, Maj. Brandon Lingle, a spokesman, said in an e-mail.

The breathing problems have become public knowledge in recent months, but the Air Force knew as early as 2000 that pilots suffered respiratory issues -- notably a dry, lingering cough -- after flying the aircraft.

And documents obtained by the Star-Telegram indicate that the Air Force declined to make a fix to the plane's oxygen system in 2005.

The so-called Raptor cough, according to scientific literature, is the result of a condition called "acceleration atelectasis."

The pilot breathes in too much oxygen too fast while the jet is performing high-G-force maneuvers, partially collapsing the lungs.

The condition may also cause pilots to become disoriented or black out. It was seen before the F-22 but not often, according to the literature.

It didn't take long for the Air Force's medical experts to link the cough to the F-22's air supply system, which provides pressurized, high-oxygen air to the pilot.

Kevin Divers, a former Air Force officer and physiology expert involved in early F-22 testing, said the medical experts and the engineering staffs of the Air Force and Boeing, which was providing the life support systems, reviewed the data and medical literature.

Boeing prepared a detailed plan for the Air Force to equip the F-22 with a digitally controlled air supply system that would have better regulated oxygen flow to the pilot at the needed levels, depending on altitude.

In 2005, the Air Force rejected that proposal, Divers said, because of the cost of changing a program already running billions over budget.

The cost, primarily to test the new system and prove its usefulness, Divers said, would likely have been no more than $500,000.

"The Air Force decided it's just an annoyance and we don't need to spend that much money just to make the pilots comfortable," Divers said in interview with the Star-Telegram.

Divers provided a copy of a Boeing technical presentation to the Air Force, as well as an e-mail exchange between himself and other staffers discussing the problems.

"It was going to cost a lot less than the millions they've spent so far" trying to explain the F-22 breathing problems, Divers said.

Air Force leaders have said their studies of the breathing issues have found no substantial evidence of any problem with the aircraft, other than a valve that causes a pressure vest to inflate too soon and may make it hard for pilots to breathe properly.

"The Air Force remains confident that the root cause of the issue can be attributed to the supply of oxygen delivered to pilots, not to contamination in or the quality of oxygen in the cockpit life support system," Lingle said in an e-mail.

Lingle said that he did not know why the Air Force rejected changes in the oxygen system in 2005 but that he would forward the question to the program manager's office.

The Air Force acknowledges that pilots may well experience acceleration atelectasis but says it does not pose a significant health or safety risk.

In an earlier interview, Lt. Col. Jay Flottman, an F-22 pilot and a physician, said the symptoms should clear up within "minutes or hours."

That view conflicts with a 2002 article written by Air Force medical experts for the service's Flying Safety magazine.

The article describes a pilot who suffered atelectasis and was restricted from flying for several days until his symptoms cleared up.

Other experts have said no studies have documented the impact of repeated incidents of atelectasis on the body.

Divers, now a consultant, said the Air Force needs to take a hard look at the F-22 oxygen system and its effect on pilot health.

"This will be a problem in the F-35 as well," Divers said. "It's just a matter of time until they get more flying time."