Oxygen Gernerator problems may go back to WWII

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

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Unread post16 Dec 2016, 09:24

I hope this isn't an old topic. I was just reading a book about the USS Enterprise CV-6 in WWII. It said that during the Battle of Midway a U.S. Dive bomber pilot had his flying career ended by lung damage from an oxygen Rebreather system. Dick Best, who planted 2 bombs, on 2 missions, against 2 separate Japanese Carriers in the same day flew a 4 hour, high altitude mission on that amazing day, June 4, 1942.

On the night of the 4th he went to bed, but began coughing up blood. The chief medical officer in Pearl Harbor concluded that his "Oxygen Rebreather " had become over heated during his long flight. "The heat created gases that turned to caustic soda, activating latent TB."

I didn't know U.S. naval aviators used oxygen rebreathers in WWII. I used chemical oxygen generators as damage control equipment when I was in the in the navy. The chemical canister became very hot, and had to be disposed of carefully. I don't know what this had to do with what happened to Dick Best, or if it has any relationship with the oxygen generation system problems with the F-22. Does anyone have any information on oxygen generators, or rebreathers in WWII, or if it has any relationship to the problems the F-22 experienced?
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Unread post17 Dec 2016, 05:34

Don't know anything about said system, but I am guessing that it was different than OBOGS. As you are probably aware, OBOGS uses [insert number based on platform] stage bleed air from a turbine/jet engine, cycles it through a scrubber (i.e. "molecular sieve") and then on to the individual crew regulators for breathing. The big problem with OBOGS is that sieve failing over time, or in other cases, toxins getting through which weren't designed to be scrubbed out. And then you get into the larger issue of flying jets at high altitude with finicky ECS/cabin pressurization systems without wearing a pressure suit. The first leads to toxic hypoxia, the second is completely unrelated to OBOGS and leads to DCS but is often lumped into "physiological episodes" or mishaps related to that factor.
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Unread post17 Dec 2016, 21:54

35_aoa wrote:Don't know anything about said system, but I am guessing that it was different than OBOGS. As you are probably aware, OBOGS uses [insert number based on platform] stage bleed air from a turbine/jet engine, cycles it through a scrubber (i.e. "molecular sieve") and then on to the individual crew regulators for breathing. The big problem with OBOGS is that sieve failing over time, or in other cases, toxins getting through which weren't designed to be scrubbed out. And then you get into the larger issue of flying jets at high altitude with finicky ECS/cabin pressurization systems without wearing a pressure suit. The first leads to toxic hypoxia, the second is completely unrelated to OBOGS and leads to DCS but is often lumped into "physiological episodes" or mishaps related to that factor.

Agree with your comments on OBOGS & DCS.

Despite what some people seem to suggest, the OBOGS & ECS in a F/A-18C/D/E/F is completely different to the F-22, even though they work on a similar principle ("molecular sieve" etc.). Some aviation physiologists were pretty confident the F-22 "physiological episodes" were not caused by OBOGS issues, and they were later proven correct.

One frustration with the "physiological episodes" is that there is little solid evidence of what actually happened. F-22 pilots do use SpO2 sensors, which will detect typical hypoxia, but not always detect toxic hypoxia. Even when they get the aircraft (F-22, F/A-18 etc.) back in one piece, there can be very little data from a physiological episode.

IMO F/A-18s should get more comprehensive environmental monitoring data recorders, to make investigating a lot easier. Hurry up and replace the sieve units would also help.
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popcorn

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Unread post17 Dec 2016, 22:42

Retrofitting an automatic emergency O2 backup system on the Raptor was money well spent.
"When a fifth-generation fighter meets a fourth-generation fighter—the [latter] dies,”
CSAF Gen. Mark Welsh
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Unread post17 Dec 2016, 23:11

popcorn wrote:Retrofitting an automatic emergency O2 backup system on the Raptor was money well spent.

Yes, money well spent. There is a bunch of reasons that automatic emergency O2 backup is a good idea, that are unrelated to the OBOGS unit itself. Dual Bleed Air Leak is one of the failures that will shut the OBOGS down.
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Unread post18 Dec 2016, 04:09

neurotech wrote:
35_aoa wrote:Don't know anything about said system, but I am guessing that it was different than OBOGS. As you are probably aware, OBOGS uses [insert number based on platform] stage bleed air from a turbine/jet engine, cycles it through a scrubber (i.e. "molecular sieve") and then on to the individual crew regulators for breathing. The big problem with OBOGS is that sieve failing over time, or in other cases, toxins getting through which weren't designed to be scrubbed out. And then you get into the larger issue of flying jets at high altitude with finicky ECS/cabin pressurization systems without wearing a pressure suit. The first leads to toxic hypoxia, the second is completely unrelated to OBOGS and leads to DCS but is often lumped into "physiological episodes" or mishaps related to that factor.

Agree with your comments on OBOGS & DCS.

Despite what some people seem to suggest, the OBOGS & ECS in a F/A-18C/D/E/F is completely different to the F-22, even though they work on a similar principle ("molecular sieve" etc.). Some aviation physiologists were pretty confident the F-22 "physiological episodes" were not caused by OBOGS issues, and they were later proven correct.

One frustration with the "physiological episodes" is that there is little solid evidence of what actually happened. F-22 pilots do use SpO2 sensors, which will detect typical hypoxia, but not always detect toxic hypoxia. Even when they get the aircraft (F-22, F/A-18 etc.) back in one piece, there can be very little data from a physiological episode.

IMO F/A-18s should get more comprehensive environmental monitoring data recorders, to make investigating a lot easier. Hurry up and replace the sieve units would also help.


Yeah, particularly with hypoxia events, time is of the essence assuming you land safely. If I'm not mistaken, medical needs to get you in within an hour of the event to properly read your blood. I've done that drill twice, both times were delayed due to outside factors……..first one being extended transit back home, second one being more of a possible DCS case (didn't actually resolve into one) after a rapid decompression at 40k+ ft, unfortunately when I put the gear down to land, I had planing link failure indications, and had to take a trap. Took almost an hour just to get towed off the runway due to runway/taxiway closures. Had to tell the wife that evening that if I started acting weird (weirder than normal at least :) ) or unusually angry, to get me in the car and to the hospital recompression chamber in Reno. Needless to say, she wasn't too psyched about my job that day.

As for other platforms, totally agree. The retrofitted F-15C/E fleet has not had anywhere close to the amount of problems the F/A-18 has had from what I understand. Strange because Mac Air built both, though apparently the OBOGS in the -15 is much newer tech. There were a lot of engineering assumptions made for the F/A-18 in the life support realm that were not accurate. One of them is that cockpit ambient air is not scrubbed in any meaningful way because the engineers (incorrectly) assumed that we would be wearing our O2 masks from engine start to shutdown. In combat in OEF/OIF, with upwards of 7-8 hour missions, LOX jets didn't even have the capacity to support that. OBOGS lets you, but most folks don't fly around for that amount of time in a low threat environment wearing the mask the entire time. Hence some of the "toxic" hypoxia events, though many more have been attributed to wearing the mask after an unannounced/undetected OBOGS failure.

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