Theory about F-22 OBOGS solution

[spazsinbad]

Saw this 'how to fix F-22 OBOGS' theory and thought it might be useful here - other than that I have no clue - and good luck.

causes of F-22 oxygen problem have been found JameLi1986

http://www.defencetalk.com/forums/air-f ... und-11978/

causes of F-22 oxygen problem have been found

http://www.youtube.com/watch?v=zvUFm9SLM_I

"Published on May 29, 2012 by orion198606
causes of F-22 oxygen problem is discovered"

[papakaz]

I thought they solved that problem when they stopped wearing chem gear on every flight.

[discofishing]

I can't understand a damn thing this guy is saying. Sounds like one of my engineering professors. Is there a written version of this?

[popcorn]

Is it possible that we are seeing different physiological maladies arising from multiple and possibly unrelated fators being attributed to some single enigmatic cause? This is beginning to look like the physicists searching for the unified theory of everything.

[f22spec]

I'm pretty much seeing that this whole thing is based off of the fact that the F-22 does high altitude violent maneuvers? After Capt. Haney's crash, all F-22 flights were restricted below 25,000 ft. However, there were still plenty more incidents (including the pilot who hit a few trees on approach for his landing), after this flight level restriction. While it might have some affect on the OBOGS system, it's not the root cause.

I can't really understand what the guy in the video is saying, though so I'm just assuming this is what he's talking about.

[spazsinbad]

'f22spec' said: "...I can't really understand what the guy in the video is saying, though so I'm just assuming this is what he's talking about." I did not realise the video had bad English. I have no sound on this computer and assumed sound was OK. Sorry about that. I'm guessing that the text is sufficient (and also explains video?). Probably explains why the text came online later?

causes of F-22 oxygen problem have been found JameLi1986

http://www.defencetalk.com/forums/air-f ... und-11978/

[river_otter]

I'm pretty much seeing that this whole thing is based off of the fact that the F-22 does high altitude violent maneuvers? After Capt. Haney's crash, all F-22 flights were restricted below 25,000 ft. However, there were still plenty more incidents (including the pilot who hit a few trees on approach for his landing), after this flight level restriction. While it might have some affect on the OBOGS system, it's not the root cause.

I can't really understand what the guy in the video is saying, though so I'm just assuming this is what he's talking about.

Strikes me as an interesting amateur theory, not complete ignorance but it doesn't entirely fit the observed incidents. I don't think it could be correct.

Oh, and Discofishing and f22spec, what he's saying is basically exactly what the text of the defensetalk.com forum post is. He's just saying it slowly in a French Canadian(?) accent.

[neurotech]

I'm pretty much seeing that this whole thing is based off of the fact that the F-22 does high altitude violent maneuvers? After Capt. Haney's crash, all F-22 flights were restricted below 25,000 ft. However, there were still plenty more incidents (including the pilot who hit a few trees on approach for his landing), after this flight level restriction. While it might have some affect on the OBOGS system, it's not the root cause.

I can't really understand what the guy in the video is saying, though so I'm just assuming this is what he's talking about.

I don't buy the explanation either. Better monitoring isn't a real solution either, or swapping to primary LOX tanks.

If disrupted/insufficient airflow to both engines from aggressive maneuvering caused the OBOGS to malfunction, there would be other indications, including a probable double engine flameout. There is a few reports of F-14s having compressor stalls & flameouts during high altitude/low-speed maneuvers. This was very obvious to the pilot/RIO however.

If physiological issues originated in the OBOGS, then switching to emergency oxygen should quickly resolve the physiological issues, but it doesn't seem to. The F/A-18 can show an OBOGS warning at high altitude if there is low outflow pressure from a leak or something. I'm not certain if the F-22 has a OBOGS low outflow pressure warning or not.

My personal opinion is that its not actually the OBOGS at all causing these issues, as they are more consistent with decompression sickness. Improved cockpit pressurization might help avoid the problems. Another option is lightweight pressure suits.

[munny]

If pilots had experienced symptoms after merely flying straight and level at high altitude and high speed then theory = wrong

You can't really work out the cause unless you know all the conditions that were common for all pilots affected (and all pilots NOT affected too). At the moment, the public have only been told one factor ... aircraft flown was the F-22

I'm sure a good ol Kepner Tregoe analysis would sort it out if they had sufficient information on the nature of the incidents.

[Raptor_claw]

causes of F-22 oxygen problem have been found JameLi1986
http://www.defencetalk.com/forums/air-f ... und-11978/

"Published on May 29, 2012 by orion198606
causes of F-22 oxygen problem is discovered"

He's wrong from the very beginning:

"Since the crash of F-22 in Alaska in November 2010. The mysterious oxygen supply problem is so far still a mystery. No one know what the real causes is. "

As has been discussed here before (extensively), the Alaska crash is well understood and involved an actual mechanical failure. ( http://www.f-16.net/f-16_forum_viewtopic-t-16562.html ). That event is unrelated to the hypoxia studies that have been ongoing for so long.

[jamesli]

Hi. I am JamesLi. I been read from news that the pressure suit they wear might be the problem . And neurotech says:
The F/A-18 can show an OBOGS warning at high altitude if there is low outflow pressure from a leak or something. I'm not certain if the F-22 has a OBOGS low outflow pressure warning or not.
---
If this is true. Then I believe my theory is wrong. The OBOGS of F/A-18 is also produced by honeywell. So they must also have such a warning mechanism.

[neurotech]

Thats just it, operational F-22 pilots don't currently wear full pressure suits. Neither do operational fleet F/A-18 pilots. That said, even the U-2/SR-71 pilots are not immune from decompression sickness (DCS). A F-22 pilot does not breath 100% oxygen during pre-flight or during all phases of the flight, so could (theoretically) be at a higher risk of DCS. A full pressure suit isn't a 'magic' solution because it all depends on the suit design. A higher internal pressure restricts movement but requires less pre-breathing. This was readily apparent on the ISS where crew had both Russian & American suits for spacewalks. The Russians had lower pressure suits, and were easier to work in.

As for the warning mechanism, I haven't heard of a OBOGS outflow leak occurring in a F-22 during flight to know for sure how the system would handle it. The F-22 Panel Mounted BRAG system is more advanced than the F/A-18 "chest" mounted regulator. The F/A-18 does not warn a pilot of a malfunctioning regulator with avionics.

The F/A-18 uses a Cobham OBOGS unit, whereas the F-22 has a Honeywell OBOGS. The F-15E Strike Eagle uses a Cobham OBOGS unit as well. The thing that is interesting is that the F-15E can fly high-altitude/high-G profiles when not heavily loaded down with stores, and has done so without 'physiological incidents' matching the F-22 pilot issues.

The problem is that they are not getting enough of a pattern to say if a pilot flies this profile in a F-22 that they'll duplicate the issue.

I think part of the issue with the Combat Edge flight suit is that it restricts breathing, especially at high altitudes, but not in a way that results in an immediate decrease in blood oxygen saturation. It is possible to have an increase in exhale CO2 without the noticeable decrease in O2 stats when breathing 100% oxygen. The Combat Edge system requires different techniques at high altitude/high-G profiles, which is not demonstrated during standard centrifuge AGSM training. Monitoring pilot respiration/exhale stats would give a clearer picture of a physiological cause.

[jamesli]

Thats just it, operational F-22 pilots don't currently wear full pressure suits. Neither do operational fleet F/A-18 pilots. That said, even the U-2/SR-71 pilots are not immune from decompression sickness (DCS). A F-22 pilot does not breath 100% oxygen during pre-flight or during all phases of the flight, so could (theoretically) be at a higher risk of DCS. A full pressure suit isn't a 'magic' solution because it all depends on the suit design. A higher internal pressure restricts movement but requires less pre-breathing. This was readily apparent on the ISS where crew had both Russian & American suits for spacewalks. The Russians had lower pressure suits, and were easier to work in.

As for the warning mechanism, I haven't heard of a OBOGS outflow leak occurring in a F-22 during flight to know for sure how the system would handle it. The F-22 Panel Mounted BRAG system is more advanced than the F/A-18 "chest" mounted regulator. The F/A-18 does not warn a pilot of a malfunctioning regulator with avionics.

The F/A-18 uses a Cobham OBOGS unit, whereas the F-22 has a Honeywell OBOGS. The F-15E Strike Eagle uses a Cobham OBOGS unit as well. The thing that is interesting is that the F-15E can fly high-altitude/high-G profiles when not heavily loaded down with stores, and has done so without 'physiological incidents' matching the F-22 pilot issues.

The problem is that they are not getting enough of a pattern to say if a pilot flies this profile in a F-22 that they'll duplicate the issue.

I think part of the issue with the Combat Edge flight suit is that it restricts breathing, especially at high altitudes, but not in a way that results in an immediate decrease in blood oxygen saturation. It is possible to have an increase in exhale CO2 without the noticeable decrease in O2 stats when breathing 100% oxygen. The Combat Edge system requires different techniques at high altitude/high-G profiles, which is not demonstrated during standard centrifuge AGSM training. Monitoring pilot respiration/exhale stats would give a clearer picture of a physiological cause.

Thanks for the very useful post!
Right now I believe in 2 possible causes:

1. The high altitude low cabin pressure + pure oxygen + high G maneuver = Alveolar collapsing / Atelectasis This have 70% possibility
2. The high altitude low air speed cause the OBOGS to malfunction. This have 30% possibility

Within 1 to 2 months we will see the report from airforce.

You say that F-15 also do high G maneuver at high altitude. That's a puzzling facts. Maybe the F-22 pilots do maneuver more frequent and more violent. I guess at high altitude(30000 feet+) the F-15 can't go beyond 6 G at most. This is my experience in combat SIMS
Any way we will wait and see the final report.
Thanks again for your profession information.

[neurotech]

Thanks for the very useful post!

Your welcome. For the record my background is in neuro-physiology and EEG technology. I did previously fly various aircraft, mainly in the back seat.

Right now I believe in 2 possible causes:

1. The high altitude low cabin pressure + pure oxygen + high G maneuver = / Atelectasis This have 70% possibility

Right reasons, wrong conclusion. High Altitude + High O2 + High Gs can also cause neurophysiological issues. The Combat Edge suit under these conditions could conceivable result in BP or ICP (Intracranial Pressure) spike in the pilot, resulting in neurological effects after the flight. The "Alveolar Collapsing" idea would have been more obvious because it would result in a drop in SpO2 during the event.

2. The high altitude low air speed cause the OBOGS to malfunction. This have 30% possibility

I still doubt the OBOGS is involved.

You say that F-15 also do high G maneuver at high altitude. That's a puzzling facts. Maybe the F-22 pilots do maneuver more frequent and more violent. I guess at high altitude(30000 feet+) the F-15 can't go beyond 6 G at most. This is my experience in combat SIMS
Any way we will wait and see the final report.
Thanks again for your profession information.

The F-15 can do high altitude/high-G maneuvers, but not with the same energy as a F-22. The pilot can still trade energy (altitude) for additional g-force.

[That_Engine_Guy]

I'd say it's not the fault of the motors providing insufficient air flow or pressure. If the engines were running out of air like that at high altitude and high AOA, they would likely compressor stall/stagnate long before bleed-air pressure/flow dropped below specification.

The pilot would know this from the loud BANG, or the loss of power in the motor(s). If anything, a condition like this would be indicated in the CSFDR or in the remaining engine control component memory. (Yes, if still somewhat intact, they can retrieve data from the engine control system chips after a crash!) It would have been obvious with any mishap that the engines had surged/stalled/flamed-out and contributed to situation.

I don't know much about the bleed-air system of the F119/Raptor, but I'm going to assume that both motors feed the common OBOGS? So that a single engine out situation would not affect Oxygen supply? This further reduces the possibilities that the Raptor's propulsion system 'slow/high' would ever be insufficient to supply the OBOGS - feeding from BOTH engines equally.

TEG