The F-22 fleet has been plagued by a mysterious air supply problem for more than a year. Strategy Page reports on what might be the solution:
The U.S. Air Force has concluded (for the moment) that the cause of the breathing problems F-22 pilots were having were caused by a defective valve on the special vests pilots wear to help them with their breathing in the low pressure of the F-22 cockpit. The vests are not being used until modifications can be made to fix the problem.
Earlier this year the vests came under suspicion because it appeared that they automatically inflated too much during high-g (gravitational force) maneuvers, making it difficult for pilots to breathe. This would be subtle, so that the pilot would not immediately notice a problem with breathing. Anything obvious would have been noticed when the vest was tested. Pilots have complained about a “strange feeling” when breathing with the vest during high-g turns but not in such a way that they connected it with the disorientation. Further examination discovered that the vest was indeed inflating when it should not have been, and causing breathing problems. The air force will make a few other tweaks to the pilot air supply system and quietly hope that the problem is indeed solved.
[. . .]
Now the air force can drop a number of precautionary restrictions imposed over the last year. For example, pilots were forced to make flights at least 24 hours apart. In training, and combat, pilots would take their F-22s up two or more times a day. The theory was that the pressure vests and acceleration atelectasis would not be a problem if pilots have at least 24 hours to recover.
Despite the breathing problems the air force continued to fly its F-22s. The decision to keep flying was made because the air supply problems had not killed anyone yet and they were rare (once every 10,000 sorties). The 14 incidents that did occur were all cases of F-22 pilots apparently experiencing problems. The term “apparently” is appropriate because the pilots did not black out and a thorough check of the air supply system and the aircraft found nothing wrong.
Here’s the initial discussion of the problem from July last year. In September, the F-22s were cleared to fly again, but they were grounded again in October.
