Leaders of an Air Force investigation into the breathing problems experienced by pilots of the F-22 Raptor told a Congressional subcommittee Thursday they have a much better understanding of what has been occurring and fixes are being made to make the aircraft safer.Major Gen. Charles Lyon said there have been no new "unexplained incidents" of F-22 pilots having "hypoxia events" since March of this year."We're certain the F-22 cockpit is a safe and effective workplace to operate," Lyon said at the hearing held by the Tactical Air and Land Forces subcommittee of the House Armed Services Committee.Under questioning from Rep. Jackie Speier, D-Calif., Lyon acknowledged that in 2005 the Air Force did not implement changes to the F-22 system that supplies oxygen to the pilot which had been recommended by its own experts to alleviate some breathing problems experienced by Raptor pilots.Speier referred to an article published today in the Star-Telegram."We have learned a lot" about the physiological effects caused by the F-22 since that time, Lyon said, and the Air Force has implemented some changes to the oxygen supply and is considering a comprehensive overhaul that would include the 2005 recommendations."The term Raptor cough didn't exist at that time," Lyon said. There were so few pilots flying, any problems noticed were not considered significant. With more flying time in ensuing years, Lyon said the problems became more frequent and noticeable.But contrary to reports of some F-22 pilots and their families, Lyon maintained that the coughing, fatigue and shortness of breath symptoms experienced by F-22 pilots were short-term and disappeared at most within 48 to 72 hours.Subcommittee Chairman Rep. Roscoe Bartlett, R-Md., said such problems "are not an indication that what's happening here is a problem with the airplane, it's just a normal part of doing what you do" with the F-22.The Air Force, following a recommendation from NASA, has taken blood samples and pulmonary function tests on all existing Raptor pilots and will be able to monitor their long-term health.Changes to a pressure vest worn by pilots that should make it easier for them to breathe will be in place by the end of the year, Lyon said. By early next year the first F-22s will be equipped with an automatic backup oxygen system and the entire fleet will be so equipped by sometime in 2014.The F-22 was jointly developed and produced by Lockheed Martin and Boeing.