Jump to content
Baseops Forums
FishBowl

T-6s Grounded; More OBOGS Issues

Recommended Posts

That's some scary shit. I don't know what they're doing differently there but I wouldn't want to be flying their tails. Have they all been rear cockpit? I know all but one were IPs... Or maybe the studs just have low SA and don't even notice the difference in the front.  

Edited by LiquidSky

Share this post


Link to post
Share on other sites
39 minutes ago, LiquidSky said:

That's some scary shit. I don't know what they're doing differently there but I wouldn't want to be flying their tails. Have they all been rear cockpit? I know all but one were IPs... Or maybe the studs just have low SA and don't even notice the difference in the front.  

I know of at least 1 stud that experienced hypoxia-like symptoms. But the vast majority have been IPs.

 

Share this post


Link to post
Share on other sites
On ‎12‎/‎6‎/‎2017 at 8:20 PM, LiquidSky said:

That doesn't make sense. Saw the fcif today and it came with specific direction that old procedure of gangloading was ineffective due to potential contaminants/toxins in the OBOGS. The emergency O2 it specifies is the only guaranteed source of pure 100% O2 hence the new boldface to pull green ring for hypoxia rather than gangloading. 

Not an expert, but thought the T-6 OBOGS was capable of producing 100% (or close to it) O2 on the ground? (not debating the boldface)

Share this post


Link to post
Share on other sites

Every O2 system has procedures for contamination.  Even LOX has steps to disconnect and pull the green ring.  Asking for more from any contaminated system will likely give more...contaminants.

Share this post


Link to post
Share on other sites

The only time I'm a doctor is when I'm talking to a hot chick at a bar... But, from what I recall the actual doctor saying, the hyperoxia (oxygen poisoning) theory explains that breathing (in this case) 95% oxygen on the ground when usually we'd be breathing ~21% might be a bad thing. Our OBOGS-equipped platforms we fly are able to deliver 95-100% O2 on the ground, and in military flight, the mask is supposed to be on during checks/taxi. So on the ground, this leads to "absorption atelectasis". (From Wikipedia) Since oxygen is exchanged at the alveoli-capillary membrane, nitrogen is a major component for the alveoli's state of inflation. If a large volume of nitrogen in the lungs is replaced with oxygen, the oxygen may subsequently be absorbed into the blood, reducing the volume of the alveoli, resulting in a form of alveolar collapse known as absorption atelectasis.

In flight, this leads to acceleration atelectasis and pulling G's can cause the base of the lung to collapse. So basically, drastically changing the composition of your alveoli on the ground, then going up and being exposed to O2 concentrations that vary between 60-80% during flights where you do multiple altitude changes is causing hypoxia (that's the theory at least).

Now take a jet like the F-15 where LOX and a diluter-demand regulator is used... At 10k' altitude, 25-50% O2 (by volume). At 20k' altitude, 40-65% O2. Finally, around 28-30k' altitude, the regulator stops diluting the incoming oxygen from the LOX bottle and 100% O2 is delivered for those altitudes and higher. LOX jets historically have a MUCH lower (reported) percentage of hypoxia events per flight hour.

Anyways, none of this is my research, but I just thought those basics were very interesting especially given the OBOGS issues in the T-6 (and across multiple other platforms as well).

Edited by tk1313
  • Like 2
  • Upvote 1

Share this post


Link to post
Share on other sites
1 hour ago, tk1313 said:

Anyways, none of this is my research, but I just thought those basics were very interesting especially given the OBOGS issues in the T-6 (and across multiple other platforms as well).

Doesn't the O2 bottle deliver 100% O2 though? So if it truly were hyperoxia that would be exactly the wrong thing to do vs. say descend and drop the mask. If they already have a new boldface directing crews to the O2 bottle I would assume that they ruled out hyperoxia and it's either foreign contaminants in the OBOGS, some form of CO/CO2 poisoning, or the OBOGS is malfunctioning and not supplying sufficient O2 quantities leading to hypoxia. 

Share this post


Link to post
Share on other sites
30 minutes ago, LiquidSky said:

Doesn't the O2 bottle deliver 100% O2 though? So if it truly were hyperoxia that would be exactly the wrong thing to do vs. say descend and drop the mask. If they already have a new boldface directing crews to the O2 bottle I would assume that they ruled out hyperoxia and it's either foreign contaminants in the OBOGS, some form of CO/CO2 poisoning, or the OBOGS is malfunctioning and not supplying sufficient O2 quantities leading to hypoxia. 

Yeah, for sure the bottle is assumed to be 100% O2. This is debatable when OBOGS is not secured on certain platforms, due to the nature of the two way switching valve, but that's a whole other argument. Anyway, the hyperoxia focus is not stating that the EPs are an issue, just that the initial oxygen that aircrew is exposed to is not helping at all. Oxygen concentrations should start low at low altitudes, and increase from there until it gets to 100% concentration at higher altitudes. This has successfully been done on LOX jets in the past. The fact that OBOGS jets now are going from 95-100% O2, then back down to around 60-80%, then once again increasing to 100% could be hurting more than just a non-linear increase in concentration based on altitude, and could explain why they (OBOGS aircraft) have far more physio events.

1 hour ago, BasicAggie said:

That is interesting, but also curious as to why it seems it's mostly Vance (plus one at Pensacola recently?)

Yeah, the hyperoxia theory doesn't quite explain the specific cases of aircraft at one particular base being bad. Hate to think the maintainers are catching all the blame, but no doubt they are being scrutinized (who worked on what airplane and when). The fact that the IPs are the ones getting hypoxic is something that I'm sure the AF team of engineers or technical experts will start to focus on.

Edited by tk1313

Share this post


Link to post
Share on other sites
24 minutes ago, tk1313 said:

 Oxygen concentrations should start low at low altitudes, and increase from there until it gets to 100% concentration at higher altitudes. 

 The fact that the IPs are the ones getting hypoxic is something that I'm sure the AF team of engineers or technical experts will start to focus on.

Interesting, what is the standard O2 delivery percentages? Is it auto-100% with weight on wheels then variable in flight based on cabin/aircraft altitude? Because pretty much of the IPs (and some studs) actually fully wear their mask on the ground. Aside from the required checks I always see it hanging when they taxi by. I would assume that in the hammerhead or holding short they put it on. 

Again for it being primarily IPs my two thoughts are it's either a backseat issue (studs normally in the front except instrument rides) or they just have more SA. 

 

Share this post


Link to post
Share on other sites

I don't have platform specific numbers with me. I know from looking at charts of oxygen analysis being done on some test jet aircraft (OBOGS) that the numbers on the ground are usually max performance (95-100%). For some aircraft, there is an OBOGS source change that happens after Weight Off Wheels that immediately shows a drastic decrease in O2% by vol, then increases back up to about 60-80%. The F-16 OBOGS O2 concentration to the face is very similar to the F-15 LOX, except it has a steeper increase at low atitudes.

A lot of pilots let their mask hang until they absolutely have to put it on, but then they are getting that mass influx of oxygen to the lungs. When it is absorbed by the blood stream, and the pilot is still breathing a very high percentage of oxygen, the alveoli start to collapse since there is not a high enough concentration of Nitrogen to retain the shape (or so the theory goes).

Luckily, with all of the OBOGS issues, they are implementing sensors in a lot of places in a lot of aircraft and this theory will be proven or disproven soon.

 

As for the T-6 IP hypoxia issues, I would have to look at the debrief from the flights/ground events. I don't know if I buy off on lack of SA because a lot of the bad cases of hypoxia end up being "Oh, I remember being cleared to land and I didn't really feel good. I remember taxiing off the runway, but don't remember actually landing the plane." If that's the case, then no amount of (lost) SA is going to help you keep 69 seconds of flight time that would have otherwise been lost due to oxygen deprivation. Personally, I'd look for 1 or 2 aircraft that have the most amount of hypoxic events associated with them and start digging deeper. In addition, it would be a good idea to do hose leak check, mask fit check, mask leak check, concentrator and regulator replacements, check for water in the system (obviously), etc for all aircrew/aircraft that had an incident. I'm sure whichever team has been tasked to deal with this issue is already knocking out that easy stuff.

Edited by tk1313
  • Upvote 1

Share this post


Link to post
Share on other sites

Navy T-45 and Vance T-6's having OBOGS issues , The F-22 also had this issue. I think the big differences between the LOX and OBOGS issues are the mx practices. Any time a component of a LOX system was replaced it required a purge of the entire system. Hot purges for Lox converters and build up and vent valves and cold purges for regulators, lines and hoses. Plus purges were also a time compliance item. Plus LOX has the deep respect of anybody who handles it, -495F grabs your attention.  Unfamiliar on mx practices of OBOGS but I wonder if future purity tests should be done during periodic intervals. 

Share this post


Link to post
Share on other sites

This is probably either not necessary (or been done) but as a lot of these aircraft are two seaters, is it possible to fly the aircraft with one pilot (on an independent O2 system) and have a sample(s) drawn from the other seat's OBOGS station to directly sample under the operational conditions when these symptoms have been reported, what exactly this system is producing? 

O2 with particulate contaminants, O2 with oil fumes or laced with carbon monoxide, directly capture what would have been inhaled by the crew and analyzed...

Not just testing the masks, filters and system itself pre/post flight but the product supplied directly to the aircrew? 

Edited by Clark Griswold
  • Upvote 1

Share this post


Link to post
Share on other sites
6 hours ago, Prosuper said:

Plus LOX has the deep respect of anybody who handles it, -495F grabs your attention.

Not to give you too hard a time, Supe, since I’m sure it was colder back in the day, but -495F is below absolute zero. :beer:

  • Haha 1

Share this post


Link to post
Share on other sites
On 12/9/2017 at 4:26 AM, mcbush said:

Not to give you too hard a time, Supe, since I’m sure it was colder back in the day, but -495F is below absolute zero. :beer:

Duh, I stand corrected, Liquid oxygen has a density of 1.141 g/cm3 (1.141 kg/L or 1141 kg/m3) and is cryogenic with a freezing point of 54.36 K (−218.79 °C; −361.82 °F) and a boiling point of 90.19 K (−182.96 °C; −297.33 °F) at 101.325 kPa (760 mmHg). It's great for cooling down six packs also.

Edited by Prosuper
extra info.
  • Like 1
  • Upvote 1

Share this post


Link to post
Share on other sites

Rumor on the streets is there was another incident at Vance today (there have been a few the last several weeks), but today it was the Vice Wing Commander and tomorrow the T-6's are stand down (supposedly).  So it takes an O-6 having issues to start taking things more seriously?  Maybe now the IP's will get a break from 7-day ops.

Share this post


Link to post
Share on other sites
1 hour ago, YoungnDumb said:

Rumor on the streets is there was another incident at Vance today (there have been a few the last several weeks), but today it was the Vice Wing Commander and tomorrow the T-6's are stand down (supposedly).  So it takes an O-6 having issues to start taking things more seriously?  Maybe now the IP's will get a break from 7-day ops.

7 day ops?  I knew white jets sucked but thats a new level.

Share this post


Link to post
Share on other sites
7 day ops?  I knew white jets sucked but thats a new level.

Surprising? We had several periods where the base was flying Monday-Saturday and then as many jets as we could fit at the local regional (GTR) on Sunday. Rinse and repeat. If they couldn't keep the base open on Saturday, then the regional was used, and others were sent cross country, but for other-than-navigation syllabus rides.

 

Great times for a FAIP, but the MWS guys weren't thrilled.

 

Share this post


Link to post
Share on other sites

Vance was similar, base open Monday through Friday, 0.1 hr hop over to KWDG Friday afternoon, and fly sorties out at KWDG over the weekend. MOAs & MTRs available on the weekend as well.

Share this post


Link to post
Share on other sites
1 hour ago, LookieRookie said:

Got briefed on this today. I'm airspeed and altitude zero in the T-6 still, but from a pilot's perspective this seems insane. I appreciate the fact that the T-6 is the Air Force's only primary trainer, but when there are already outstanding TCTOs for EFIS displays catching on fire and faulty ISS, and now OBOGS issues as severe as the most recent one we were briefed on, is the Air Force leaning too far forward? I never imagined I would be expected to fly an airplane with this many outstanding safety of flight issues, and I came from the C-5. I don't know if the most recent event is under an active safety investigation and therefore don't want to get too far into it, but suffice to say that if the affected pilot had been solo, he would be dead. Every time a base stands down, it tells me that they felt they crossed some sort of line, and when AETC releases a new FCIF or terribly written boldface, all they are doing is redrawing the line a little bit further. I honestly feel that with the FCIF allowing flight with dropped masks in light if the most recent event, you can't move that line much farther. It upsets me because it tells me that now the line is death. The Air Force won't call knock it off unless one of us gets killed.

Am I crazy? Is there anyone else with the same sort of ideas running around their head? Also, any Navy guys here have experience with the T-45? How did the Navy handle its OBOGS issues?

UPDATE: http://www.aetc.af.mil/News/Article/1429270/19th-air-fo/

Maj Gen Doherty orders an ops pause.

Edited by zachbar

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



×