Mitt Romney says he wants to re-open production of America’s topline stealth fighter program. One problem: The Air Force still isn’t sure why the planes were intermittently choking their pilots for more than a decade.

Thanks to a big assist from teams of Navy divers and NASA scientists, the Air Force believes it has figured out how to keep the F-22 Raptor’s fighter jocks safe, after 12 years of disturbing incidents. That’s the good news from today’s Congressional hearing on the Raptor’s long history of causing mysterious, and potentially fatal, breathing difficulties.

The bad news: The Air Force doesn’t know what’s really going on in the F-22 pilots’ bodies that make them experience dizziness, confusion, memory loss, blackouts and, over the longer term, chronic coughing and fatigue. Nor do they understand why the stealth jet is producing these symptoms. Through trial and error the flying branch and its Navy and NASA pals have figured out what the experts say is the best remedy to these dangerous symptoms.

But Air Force officials admitted to the House Armed Services Committee that they continue to be confused about what physical condition is actually causing the lethal effects. Service leaders have stopped using the term “hypoxia,” which means oxygen shortage, instead referring to “hypoxia-like symptoms.” Low blood sugar, dehydration and hypocapnia — a shortage of carbon dioxide in the blood — could also cause pilots to get dizzy and black out, testified Maj. Gen. William Lyon, who heads the service’s F-22 investigation.

In other words, the current fixes — an improved pressure suit for the pilots, a new backup oxygen system plus the removal of a faulty air filter, among other adjustments — are really only band-aids.

The Air Force is confident that, with the fixes, the Raptor cockpit is a comparatively “safe and effective place to work,” Lyon said.

But the Air Force can’t honestly say its roughly 180 Lockheed Martin-made F-22s are “100-percent safe,” as Brig. Gen. Matthew Molloy, the commander of a rotational Raptor base in the Pacific, claimed last month.

That uncomfortable truth should add some context to Republican presidential candidate Romney’s vow to re-open Lockheed’s defunct F-22 production line and produce more of the radar-evading jets, which cost nearly $700 million apiece to design, build, upgrade and operate.

The Thursday hearing shed new light on the F-22′s history of harming its pilots and the Air Force’s years-long efforts to figure out why. Lyons told Maryland representative Roscoe Bartlett, the Republican chair of the Subcommittee on Tactical and Air Land Forces, that the first case of Raptor-pilot breathlessness occurred in 2000, when the F-22 was still in testing. Raptor pilots suffered just six hypoxia-like incidents between 2003 and 2008, in part because there were so few of the jets flying, Lyon added.

In 2005 Boeing proposed to improve the Raptor’s oxygen systems, an offer the Air Force declined because at the time hypoxia-like symptoms “were at a small level,” Lyon said. He insisted recent changes to the F-22 have resulted in safety improvements equivalent to the Boeing-proposed upgrades from seven years ago.

The number of pilot chokings spiked from 2008 to 2011 as more new F-22s rolled out of Lockheed’s Marietta, Georgia, factory, Lyon explained. There were another dozen hypoxia-like incidents in those three years, apparently not counting Capt. Jeff Haney’s fatal crash in Alaska in November 2010, which the Air Force continues to blame on Haney despite evidence he blacked out. Lockheed recently settled a lawsuit by Haney’s widow.

Overall the Raptors strangled their pilots 27 times per 100,000 flight hours, nine times the rate of other U.S. warplanes. Weirdly, ground crews suffered occasional symptoms, as well. Equally strange, only two F-22 facilities out of eight ever experienced any problems.

In May 2011 the Air Force grounded the entire F-22 force — numbering six combat-coded squadrons in Alaska, Hawaii, Virginia and Florida plus forward bases in Japan and the United Arab Emirates — while the flying branch investigated the pilots’ symptoms. The investigation, led by retired general Gregory Martin, ruled out low blood sugar and dehydration and focused instead on hypoxia and hypocapnia. Both conditions are attributable to the aircraft’s systems rather than solely to pilots’ behavior.

Suspecting air-supply contamination, the Air Force added a charcoal filter to the Raptor’s oxygen-generator. The filter made the problems worse, adding black phlegm to the pilots’ signature “Raptor cough.” The F-22s returned to flight in September last year, albeit with altitude restrictions that Lyon said represented an “acceptable level of risk.” But two pilots disagreed. Maj. Jeremy Gordon and Capt. Josh Wilson refused to resume flying a jet they deemed too dangerous.

In an interview with 60 Minutes in May, Gordon and Wilson claimed that the “vast, silent majority” of F-22 pilots lived in fear of the airplane. Facing Air Force reprisal, Wilson sought whistleblower protection. But the flying branch did agree to remove the harmful charcoal filter.

The F-22s were back in the air — and busier than ever in training exercises and overseas deployments. But the Air Force still really had no idea exactly what had caused the pilot blackouts.

Desperate and under increasing pressure from the Pentagon, the Air Force brought in outside help, including Navy divers experienced with oxygen deprivation and a team of NASA engineers and scientists, Lyon said. In short order, the flying branch found problems with a valve on the special vests worn by F-22 pilots to counteract the effects of thin air and high G forces. Under certain conditions the valve could restrict airflow to the aviator’s lungs, the Air Force concluded.

The Air Force tweaked the vests and also began installing a backup oxygen system, with all 180-plus F-22s scheduled to get the backup gear by the middle of 2014. In the meantime, NASA’s investigation continued. In addition to studying the Raptor’s oxygen woes, the NASA group also scrutinized the Air Force’s approach to solving the jet’s problems.

The space agency endorsed the Air Force’s filter, vest and backup oxygen plans — an “ah-hah moment” for the service, Lyon testified. But in a report issued two weeks ago, NASA also found the flying branch wanting in some regards. The space agency warned against what it called the “normalization of deviance,” NASA investigator Clinton Cragg testified alongside Lyon. In other words, over time pilots and bureaucrats risk viewing preventable dangers as just a routine part of the job — a phenomenon that partially explains why the Raptor’s oxygen woes have dragged on for 12 years.

Cragg told the House subcommittee that the Air Force’s investigative process “could have been more efficient.” He said he wants to see additional reviews of the F-22′s pilot gear and another formal assessment of the flying branch’s attempts to address the hypoxia-like symptoms. The implication is that the fixes to the Raptor’s systems aren’t perfect.

There have been no hypoxia-like symptoms in the F-22 force since March, Lyon revealed. But in light of the uncertainty surrounding the Air Force’s investigation, it should surprise no one if America’s stealth-fighter pilots start blacking out again.