Combat Edge anti-g ensemble might be causing Raptor’s oxygen

Anything goes, as long as it is about the Lockheed Martin F-22 Raptor
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neptune

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Unread post06 Jun 2012, 01:54

http://www.flightglobal.com/news/articl ... es-372642/

Combat Edge anti-g ensemble might be causing Raptor’s oxygen woes
By: Dave Majumdar Washington DC

The Combat Edge upper pressure-garment worn by US Air Force pilots flying the Lockheed Martin F-22 Raptor might be the cause of the fifth-generation fighter's oxygen maladies, sources say.

While pilots need counter-pressure from the vest-like pressure garment to exhale at low cabin pressures found in the Raptor's cockpit, the Combat Edge and associated breathing systems might be providing too much pressure especially under g-loading.

"It just seems a little weird to breathe of off this thing," one source says. "Because you can't expand your lungs as easily because you have something restricting you."

The extra load imposed on the pilots by the added pressure under g-forces could be causing them to "over-breathe the system".

A compounding factor may be a condition known as acceleration atelectasis. The condition causes the pilot's lungs to have trouble bringing oxygen to the blood system because pure oxygen--93% oxygen in the Raptor's case-- and high gravity loads set up the pilots for a condition where the air sacs in the lungs suffer partial collapse.
...

Earlier tests would not have caught the problem because the breather device used to test the Combat Edge system does not compensate for pilot's lungs being unable to expand as readily. The breather device always draws the same volume of air.

A lack of ability to test for restricted expansion kept the condition from being seen as a problem. The restricted breathing could lead to hyperventilation symptoms or even bigger issues if the pilot is suffering from acceleration atelectasis.

However, the source says, the pressure-garment problem has been a known concern since at least 2000 when a similar garment provided by Boeing was being flown. But at that time, the USAF did not believe that the extra pressure was a serious concern. Now however, the USAF is starting to believe that the Combat Edge is behind the Raptor's woes. But while current USAF research is pointing to the Combat Edge as the primary culprit behind the F-22's maladies, the source says that it is probably only part of the problem.

Unlike U-2 pilots, who fly only after a several-day rest period after each flight, F-22 pilots will sometimes fly more than once a day. This means that the pilots are flying before they fully recover from the effects of acceleration atelectasis. Thus when they are g-loading in flight, they are further exposed to the pressure from the Combat Edge and their breathing device. The exposure to maximum oxygen while already suffering from acceleration atelectasis means even less oxygen saturation for the pilot. The sum total can result in the "hypoxia-like" physiological symptoms that have been vexing F-22 pilots for the past year.

"It was an annoyance issue, but an annoyance issue after you were on the ground," the source says. "But there is no exposure limit on these guys and early on a double turn was a rarity."

Ironically, some of the safety measures that the USAF added after the service lifted the grounding such as flying with a negative-pressure carbon-filter--which is having oxygen pushed through it under pressure-- and with the oxygen system set on maximum at all times probably exacerbated the problem, the source says.

One possible solution might be the new pressure-garment designed for the Lockheed Martin F-35, which could potentially solve the some of the pressure issues. But F-22 crews may need to take a 24h break between flights, the source says. That would cause a sortie generation problem, however.

..... Analysis of the data is getting us closer to identifying a root cause or causes, although we don't have preliminary results or a projected completion date to share at this time," the USAF says.

Meanwhile, pilots flying the F-22 have not suffered any new unexplained hypoxia-like physiological incidents in nearly three months, the service says.

"We haven't had an unexplained physiological incident since 8 March," the USAF says.
:idea:

Another take by same author;

http://www.flightglobal.com/blogs/the-dewline/
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pants3204

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Unread post06 Jun 2012, 02:11

Just how much more g-loading are pilots going through in the F-22 in comparison to the F-16 for example? What level of gravitational force would induce something like acceleration atelectasis?

And, do pilots of other high-performance aircraft use these suits?

I mean it makes sense that that could be a problem.

How does this explanation account for the crew members having symptoms?
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munny

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Unread post06 Jun 2012, 08:44

While the theory satisfies the question of why F-22 pilots are affected but not other aircraft pilots, there is still not enough information to say its the cause. Like the theory in another recent thread, this one can be discounted if the issue happened while some pilots were merely flying straight and level.

Damn, how high do these things fly compared to other aircraft and how many G's are they pulling up there?
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Unread post06 Jun 2012, 13:40

Do Super Hornet pilots fly with this system?? If so, that's interesting....
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papakaz

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Unread post06 Jun 2012, 19:37

So the reason the Raptor Cough happens is because their G-suit is too good...Does anyone know of a possible comparison between ATAGS/Combat Edge and other anti-G gear in use today?
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Unread post07 Jun 2012, 07:14

southernphantom wrote:Do Super Hornet pilots fly with this system?? If so, that's interesting....

Yes, the Navy Combat Edge has been out a while and pre-dates the F/A-18E/F fleet introduction. The Super Hornet can go past 50,000 with a waiver for flight tests, but not fleet operations for a variety of reasons.

I'm not sure the Max G at high altitudes, but its likely to be less than F-22 for performance reasons.
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Unread post07 Jun 2012, 07:27

munny wrote:While the theory satisfies the question of why F-22 pilots are affected but not other aircraft pilots, there is still not enough information to say its the cause. Like the theory in another recent thread, this one can be discounted if the issue happened while some pilots were merely flying straight and level.

Damn, how high do these things fly compared to other aircraft and how many G's are they pulling up there?


The issue of how this happens in straight and level flight is a strange one. If somebody went to the flight surgeon and said "I was pulling 9Gs and started to grey out..." that would be obvious. If a pilot said "I flew ACM at 9Gs and felt hypoxia like symptoms 20 minutes later" that would be harder to pinpoint. Cognitive Impairment can occur with repeated high-G maneuvers during a flight due to cumulative effects. This would not be unique to the F-22 however, and with these issues happening with experienced fighter pilots coming over from F-16 its unlikely they are mistaking ALOC for these "physiological incident"
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Unread post14 Jun 2012, 19:42

Interesting story to just come out......
ABC new reports: F-22 Fighter Pilots Told to Ditch Pressure Vests; Mystery Problem Unsolved (by Lee Ferran ABC news)
Pilots for the U.S. Air Force's F-22 Raptor fighter jets have been ordered to take off a -portion- of their flying suits, specifically the G-suit vest, during routine training missions as the service continues to investigate a rare but mysterious breathing problem some pilots have experienced in the $420 million-a-pop jets.
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Unread post15 Jun 2012, 23:04

CNN just aired a small bit on Wolf Blitzed's Situation Room.

Here's the gist of it:

They said F-22 pilots had "breathing problems" ~10x more often than other fighter pilots. They also said the USAF is closer than ever to solving the puzzle and that the [Combat Edge] was the likely culprit, saying that it was "inflating" (which I assume meant that it was "force-feeding" breathing air) when it wasn't supposed to, interfering with the pilot's normal breathing. (Maybe Combat Edge is an example of an innovation that works better in theory than it does in practice?)

They also showed Sprey ( :roll: ) throwing in his dubious 2¢ by intimating that the "toxic" stealth coatings are to blame, which would explain ground crews getting sick and the low-altitude/low-G incidents. A USAF "source" countered by saying that the coatings are not "toxic" and that some of these "hypoxia" incidents are likely psychogenic.
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Unread post16 Jun 2012, 01:23

http://www.sfgate.com/cgi-bin/article.c ... -M5KPT.DTL

SFGate
Back to Article
F-22 Pilots Told to Stop Wearing Pressure Vest Routinely

David Lerman and Tony Capaccio, ©2012 Bloomberg News

Wednesday, June 13, 2012

(Updates with comment from Air Combat Command surgeon general in seventh paragraph.)

June 13 (Bloomberg) -- The U.S. Air Force has instructed pilots of the F-22 Raptor to stop wearing a pressure vest during routine flights as the service continues to investigate oxygen- deprivation incidents on the Lockheed Martin Corp. fighter jet.

"Recent testing has identified some vulnerability and reliability issues in the upper pressure garment worn by F-22 pilots," Lieutenant Colonel Edward Sholtis, a spokesman for the Air Combat Command, said today in an e-mailed statement. He said the Air Force is working to correct the problem.

The Air Force has been trying to figure out why F-22 pilots have suffered from hypoxia-like symptoms that include dizziness and disorientation. There have been 11 unexplained incidents related to a lack of oxygen since the plane resumed flying last year after a four-month halt for safety concerns.

"The upper pressure garment is not 'the' cause of physiological incidents, and we still have other variables to work through before we can determine what the major factors are and how they interact to produce the number of unexplained incidents we've seen," Sholtis said.

The Air Force has been studying whether pilots are getting enough oxygen and whether the air they breathe may be contaminated.

The pressure vest is the upper portion of the "G suit" worn by pilots to withstand high levels of acceleration, or "G" forces.

'Tight-Fitting Garment'

Brigadier General Daniel Wyman, the Air Combat Command's surgeon general, said in an June 11 interview that investigators are examining all "life-support garments" used by F-22 pilots.

While Wyman gave no hint of a flaw in the pressure vest, he said investigators found "the life-support equipment was not appropriately fitted" for pilots "and actually may have restricted their ability to breathe."

"It was like a tight-fitting garment that would not fully allow you to expand your chest," he said. "We've gone back out to the field, insuring that everyone was wearing their equipment appropriately."

Sholtis said the Air Force is looking at the flight suits worn by F-22 pilots in combination with the pressure vests.

Layering Equipment

"Testing has determined that the upper pressure garment increases the difficulty of pilot breathing under certain circumstances," Sholtis said. "We're also looking at the layering of other aircrew flight equipment as contributing to that difficulty."

The Air Force isn't ready to label the vest as a cause of the hypoxia symptoms because officials are still gathering data, according to a government official briefed on the latest information.

The service is looking in particular at the flight suits, worn in combination with the pressure vests, by F-22 pilots at Joint Base Elmendorf-Richardson in Alaska and at Joint Base Langley-Eustis in Virginia, according to the official, who spoke on condition of anonymity because the investigation is being handled in private.

The official said investigators suspect the combinations may be restricting a pilot's ability to expand his chest and take a full breath.

The Alaska-based pilots wear an arctic survival suit intended to protect them after an ejection over cold terrain. Those based in Virginia wear anti-exposure suits as protection after an ejection over cold water. While similar to a wet suit, it doesn't fit as tightly.

The pressure vest serves as protection against both G forces and a rapid decompression at high altitude.



--Editors: Larry Liebert, Bob Drummond

To contact the reporter on this story: David Lerman in Washington at dlerman1@bloomberg.net

To contact the editor responsible for this story: John Walcott at jwalcott9@bloomberg.net

http://sfgate.com/cgi-bin/article.cgi?f ... -M5KPT.DTL
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Unread post16 Jun 2012, 03:10

Does anyone know the nomenclature of the two types of suit mentioned in the article:

The Alaska-based pilots wear an arctic survival suit intended to protect them after an ejection over cold terrain.
Those based in Virginia wear anti-exposure suits as protection after an ejection over cold water.
While similar to a wet suit, it doesn't fit as tightly.
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Unread post16 Jun 2012, 07:14

A poor fitting Combat Edge flight suit would make sense. If a pilot can't exhale excessive CO2, that would make them feel breathless with 100% oxygen being supplied.

Another factor that the F-22 has a panel mounted oxygen regulator, whereas previous (* Navy?) jets use a "chest" mounted regulator. This would account for the F-22 having more incidents than other jets.

I'm not sure of the arrangement in the F-35 but it is derived from the F-22 system. It is possible that the test pilots have avoided high altitude, high-G profiles so far in the test flights.

Edit: It came to my attention that F-16 C/Ds have panel mount regulators, but they are different system than the F-22 & F-35 BRAG. The newest USAF F-16 Block 50(FY97+) have OBOGS made by Cobham. The OBOGS equipped F/A-18s have the chest mounted regulators and are a significantly different system.
Last edited by neurotech on 16 Jun 2012, 20:22, edited 1 time in total.
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Unread post16 Jun 2012, 10:41

I keep thinking about something that I believe Dozer said a couple of years ago on fencecheck:

"I know a number of guys that tested the new liquid g suit, there were a few neutral comments on it and a lot of very negative comments. Its 180 degrees different from how we currently train ourselves to deal with g forces. I've heard guys say it might work on a new pilot who's never been trained in the "old" way, but lots of guys greyed or blacked out with it, I get the feeling it would be extremely dangerous for us to transition into it."

I wonder if the difference between the "old" and the "new" guys may be causing some issues for some people and none for other pilots?
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Unread post16 Jun 2012, 19:56

scruffer wrote:I wonder if the difference between the "old" and the "new" guys may be causing some issues for some people and none for other pilots?


That is a likely scenario, and not disputing Dozer, but there has to be more than the old vs new pilots. If that was the only major factor, then test pilots would be disproportionately affected since they are older, and have significant experience in other jets compared to operational F-22 pilots.

A known incident of a test pilot, LtCol David Cooley, flying for Lockheed, experienced A-LOC, a physiological incident and tragically died during ejection.
The MTP’s anti-g garments, to include the Advanced Tactical Anti-G Suit (ATAGS) and the Combat Edge anti-g vest were properly inspected by Aircrew Flight Equipment personnel prior to the mishap mission. Post-mishap operability tests confirm each item functioned as designed during the mishap test mission

I'm not sure of other incidents involving experienced test pilots an physiological incidents.

I still believe that breathing technique is critical above 40,000+ when using the Combat Edge suit. Improved training may help improve this and reduce the number of incidents.
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Unread post16 Jun 2012, 21:23

A known incident of a test pilot, LtCol David Cooley, flying for Lockheed, experienced A-LOC, a physiological incident and tragically died during ejection.
[/quote]

I don't recall the details, but Cools did not die because of a physiological incident.
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