Wednesday, August 01, 2012

The F-22 Is Cured, We Hope

July 31, 2012: 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.

At first it was thought that the pressure vest problems might be linked to recently reported instances of excessive coughing by F-22 pilots. It's being called "Raptor Cough" and is actually a known condition (acceleration atelectasis) for pilots who have just completed a high speed maneuver. But it appeared to be showing up more frequently among F-22 pilots. The F-22 pilots are perplexed and a bit nervous about their expensive and highly capable jets and are reporting things they earlier thought little of. But a close look at vest use revealed that the vests were quietly acting up nearly every time there was a breathing problem. This ended over 16 months of restrictions on F-22 use and increasingly frantic efforts to identify the source of the problem and fix it.

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.

There have been nearly 30 of these "dizziness or disorientation" incidents in the last four years, with only 14 of them serious enough to be called real incidents. Only one F-22 has been lost to an accident so far and while that did involve an air supply issue, it was caused by pilot error, not equipment failure.

Among the precautionary measures taken was spending $7 million to install commercial oxygen status sensors in the air supply systems of F-22 fighters. The air force also spent $20 million on automatic backup oxygen systems for 40 of its F-22s. This was a safety measure for heavily used F-22s and an attempt to capture data from one of the rare "events" that the pilots have had with their breathing.

The F-22s comprise the most powerful component of the air force's air combat capability and the brass were eager to find out what was wrong. The air force recently received the last of 187 F-22s that will be built. Production was limited because these aircraft were too expensive. It was very embarrassing that their safety should be threatened by something so basic as the pilot air supply.


Just in the nick of time.


Post a Comment

<< Home