Monday, May 4, 2015

GLOC is not a pistol but will kill you just as dead

The genesis for this post came as I was searching on YouTube for a video on how to maintain my Glock Model 22.  As I was typing in my term, I was presented with a wide variety of videos purporting to show the hilarity in GLOC (G-Induced Loss of Consciousness).  I watched a couple videos and failed to see much hilarity, but I guess that’s just me.

I did, however, think the subject was worthy of a posting.

So, There I was….*

I’m at Holloman as a IP at Lead-In Fighter Training (LIFT).  It’s the early ‘80s and the Eagle has been around for a few years and the F-16 is being widely deployed thanks to the Reagan Buildup.  As with the development and deployment of any new aircraft, fighters especially, there have been some accidents.  It’s been particularly centered on the F-16, enough to earn the jet the politically incorrect sobriquet of “Lawn Dart”.  

“Want an F-16? Buy land in Utah!”  Hill AFB outside Ogden is one of the first F-16 bases.
Aircraft Safety and Crash Investigation techniques have improved over the years and many of these crashes did not seem to be caused by mechanical failures yet the impact angles were quite steep with no apparent attempt by the pilot to eject.  This led to the hypothesis that the pilot had somehow become incapacitated.

The Air Force knew that high Gs could cause unconsciousness and had for years.  In fact, one of the first US fighters, the Sopwith Pup was capable of pulling and sustaining 8 Gs.  I wonder how many fatalities over the years written off to mechanical failures or just plain "unknown" were, in fact, GLOC caused?
Source: Photo by Alan Wilson on wikipedia

The Spitfire, in WWII, was outfitted with two sets of rudder pedals, one set above the others.  The theory was that elevating the legs would assist in keeping the pilot’s blood where it was needed, in the brain.

This guy is building these for a simulator, but he seems to be going for accuracy.

The big difference with the 4th generation fighters (F-15, F-16 and F/A-18) was that the G onset rate is so great, that the pilot is not provided the reaction time to begin a straining maneuver.  He is rendered unconscious in just a couple of seconds, so fast I’ve heard the stick in the F-16 referred to as a “sleep switch”.  

Snap it back, take a nap.

The “nap” would cause the pilot to lose consciousness and would usually result in his releasing the stick which would cause the aircraft to return to unload (the G load would reduce).  After a few seconds, usually around 15, the pilot would regain consciousness.  However, studies conducted at Brooks AFB indicated that though the pilot was conscious at this point, he was incapable of coherent thought or action for between one and two minutes.  To put that in perspective, an aircraft travelling at 480K will travel 8 miles every minute.  One to two minutes can be, quite literally, forever in a GLOC situation.  Watch how long it takes this guy to get back up and running.

Physiologically why does the pilot take a nap?  I’m sure some of the medically trained CDD Cognescenti can explain this off the top of their head, but I’m not a Doctor, nor have I played one on TV, so:

“Visual symptoms of Grey-out or Peripheral Light loss (PLL) also referred to as ‘tunneling or veiling of vision’ and Black-out or Central Light Loss (CLL) are due to disturbances in the circulation of the inner-most layer of eye, the retina. These changes may precede cerebral circulatory disturbances, as the blood flowing into the retinal arteries  have to overcome an Intra-Ocular pressure of about 20 mm Hg. As the mean arterial pressure in the head and neck drops down to near Intra-Ocular pressure level, retinal arteries start collapsing at the periphery and later even the central retinal artery collapses resulting in grey out and black out, respectively. While visual symptoms occur, the blood may still be flowing into the brain, if the acceleration onset rates are gradual. However, within 6-12 seconds of the onset of acceleration forces of combat manoeuvres, reflex changes, triggered by the blood starved brain, occur in the circulatory system. These result in vasoconstriction, increased force of contraction of heart and increased heart rate, in turn trying to maintain blood supply to the brain. If the blood supply to the brain falls below critical levels, the aircrew may have ALOC or GLOC.”

Running that through Google Translate to translate from “Flight Medicinease” to “Fighter Pilot”, I come up with “The brain needs oxygen, carried in the blood, to think.  Since flying and fighting a fighter requires thinking, the pilot needs blood in the brain.  If all his blood is in his feet, he’s in deep doo-doo.”

So the Docs at Brooks figured out that a pilot has a 5 second window to be fully into the straining maneuver before the normal oxygen supply in the blood is depleted.  This straining maneuver, called an L1 or M1 back in my day (I’ve heard reference to a Hook maneuver in more modern video), involved tightening the muscles in your legs, constricting your stomach muscles, and taking quick gulps of air, then exhaling in short blasts.  All that served to oxygenate your blood and keep as much of it as possible in your upper body.

Given the destructive nature of a GLOC while airborne, the USAF established a school at Brooks to teach pilots how to effectively prevent it. ( I assume the Navy and Marines did also given the above video, just don't know where.)

The plan is to send LIFT IPs to Brooks to learn the physiology of GLOC so we can teach our young fledglings how to perform the M1 as well as how to recognize an improperly performed one.

Digression Alert (Fledgling is a young bird that has just fledged.  Fledged is the stage in a young birds life when the feathers and wings are sufficiently developed for flight.  Ergo, our students are fledglings.)

“Stay on Target, stay on target.”

The training mechanism for this course is a centrifuge.  

While not exactly like the Brooks Centrifuge, it was quite similar.  No glass though so you couldn't see out.

The centrifuge at Brooks is outfitted with a F-16 seat (the reclined version of the Aces II Zero, Zero seat.) and control stick which controls the G load as well as the onset rate. And no Bond Girls. 

The onset rate is programmed to be the same as an F-16’s. The HUD is a simple CRT with a Pipper and a Mig-21 silhouette which goes up and down the screen depending on whether the program wants you to pull more or less Gs.  When the pipper is centered, you are pulling exactly the G level the instructors want.  It also gives the victim student something to think about other than how much this sucks. (Rather a lot, BTW.)

The centrifuge is built such that it will always come to a complete stop right beside the door.  While convenient in that you don’t have to walk far to get in or out, the actual reason is to allow quick access to the pilot in the event of an incident.  It is very confidence enhancing to notice that there’s a defibrillator hanging from the wall right beside the door.  Just in case.

So, I’ve been selected to be in the second group of IPs from Holloman to go TDY to Brooks (San Antonio) and participate.  Fighter Pilots as a rule do not visit Brooks.  It is home to the USAF’s Flight Medicine School, so is thickly populated with Flight Surgeons and Flight Surgeon wannabees just looking for some new way to ground a Fighter Pilot.  

Being ordered there to participate in training where I’ll be hooked up to an EKG, while being subjected to considerable physiological stress and being monitored by several Flight Surgeons seems to be a prescription fraught with danger.

We arrive at the facility and begin the academic portion of the program.  Essentially, it’s the same information presented above, spread out over two days.  Bore. Ring.

The third day will be taken up with the “flight”.  While I don’t perfectly recall the profile, I think each flight was about 10 minutes long.  The victim student would get strapped in, and the centrifuge would be turned on.  This was automatic and set to spin at about 1.5 G,  not enough to cause problems, but enough to get the fluids stabilized in the inner ear.  Early profiles had problems with students feeling tumbling effects when they went from a stop to 9 G’s in a second.  It’s very hard to do a good straining maneuver when you’re tumbling head over heels and puking your guts out.

So, you’re spinning at 1.5 Gs while getting acclimatized and the instructor talks you through the switchology and answers any questions you might have.  Then the profile begins, the first maneuver will be a constant 4 G pull for 3 minutes.  

4 G is about what a person will experience on one of the most aggressive roller coasters.  It shouldn’t be hard, but can, over time, cause a GLOC if the straining maneuver isn’t effective.  Mine is.

Back down to 1.5 Gs, while the instructor critiques your straining maneuver.  The second profile will be a max of 6 Gs for a minute and a half.  However, the G load will go up and down in a random pattern simulating the loading and unloading that would happen in an actual engagement.
I’m able to handle this without too much problem, although the onset rate is way more than I’d experienced in the F-4 or AT-38.  Got a little behind on one pull and started to gray out.  Fortunately, as my vision started to dim, the profile called for an unload and I was able to get back on top of it. 

So, by now, I’ve been above 4 G for four and a half minutes.  The suckage meter is climbing.  But other than onset rate, the G’s haven’t been anything I haven’t experienced before, so I’m doing ok.  

The next profile will be 8 Gs for 20 seconds.  With one exception, that will be more Gs than I've ever pulled and certainly for a longer period.

But, I know it’s coming so I’m ready for it.  Get on the strain and pull the pole.  20 seconds turns out to be a VERY long time.

Back down with two profiles left to go.  The next one is a straight 9G pull for 15 seconds.

I’m interested in this as 9G is the limit for both the Eagle and the F-16.  While this is still early in my Holloman tour, I want one or the other as my follow on assignment.  This profile will let me know if I actually can hack the aircraft.

Get up on my straining maneuver and pull back on the stick.  Suckage meter is bouncing off the peg.  Feels like my heart is coming out my back and the muscles on my legs (the only unsupported part of my body) are being ripped off. 

Finally 15 seconds expires and I’m back to 1.5 Gs.  At that G load, it feels like I’m floating.  Only one profile left to go.  For this one, I’ve got to look over my shoulder, my choice left or right, pull on the pole and make a bandit call while executing a simulated break turn.  

The profile is 10 seconds long and the Bandit call requirement is designed to complicate the straining maneuver as you have to expel air to talk.  If you don’t work the inhale/exhale while talking sequence correctly, you can take a nap.

There was a consequence for taking a nap in the simulator, but I don’t remember what it was.  I think it was redo the ride.  All I remember, just prior to the last profile, was how much I didn’t want to do this again.

Into the strain, on the G, bandit call made, and an hour and 45 minutes later in Central Suckage Time, the G comes off and I’m done.

Get back home, and am changing clothes in my bedroom when my new bride looks at my behind and asks me what I’d really been up to in San Antonio.  I was puzzled until I looked in the mirror.  My backside was covered in what looked like hickeys.  One of the downsides to having blood forced where it shouldn’t go is the capillaries tend to rupture, leaving bruises.  I explained this to my bride who was somewhat skeptical, until she talked to some of the other wives and found similar stories.

Not a picture of me!  I guess they've actually got a name now,  The source calls them "Geasles".

I’ve finished my tour and am headed to Kadena, but have gone back to Holloman after RTU to get the family moved.  Stop in at the squadron to check on friends and events.  One of the projects the wing had undertaken was the construction of a centrifuge there.  The LIFT students would fly a similar profile as part of the LIFT curriculum which would better train them for their follow on jet.  I asked how that was going and was told it had been put on hold.  Seems the building contractor misread the blueprint or made a mistake in measuring the room.  The centrifuge would spin freely for ¾ of a revolution before hitting a wall, literally.

General information was gleaned from and  



  1. Well that dredged up a few memories. Fun post and very well done, Juvat. The world needs more fighterpilotese, and less of the other stuff (the last phrase above may have been garbled, however. Doo-doo?).

    The first time I ever heard of the term gloc was while examining a pitifully small pile of Hornet wreckage in the hangar bay.

    I have a scar above my starboard eye that I collected during my stint as a gloc research technician (autonomous non-instrumented test dummy) at NAMI. Turns out that improperly secured gear in the cockpit also accelerates at n x 9.8 m/s squared. Who knew?

    The little hickeys are also called petechia (PUH-tiki-eye).

    1. Thanks.
      Doo-Doo. Well, Sarge runs a family friendly establishment.
      Went through UPT at Laughlin at the same time the Iranian AF was sending their pilots through. On a solo ride, a pair of them decided to modify the parameters for a Cuban 8, rotating it 90 degrees in the vertical. An immelman, roll rightside up, an immelman, Split S, roll inverted, Split S. 90 degrees through the second Split S, they went supersonic and without the stick authority and altitude available, went into the ground almost completely vertical. The Wing King was furious and marched all of us through the hangar to look at what was left. The only truly recognizable piece was one of the mirrors, which appeared to be intact. "Pitifully small pile" is an apt term.
      Thanks for the Medical terminology, but I think I'm going to stick with "hickeys", reduces the "HUH?" response.

    2. juvat/

      My wife the RN would insist you use petechia. :)

      I had two Iranians in my class also at Laughlin. And boy would their Iranian Liason/"minder" officers chew their arses if they screwed up!

    3. I'm sure she would, but then again, she'd know what I was talking about.

      "Camels to Jets" was the usual riposte to tales of their screw ups. And there were the urban legends of being told that the cruise control on their black Trans Ams was "like an autopilot" and having them set it and climb in the back seat for a nap. And the one about the Shield shaped sign with the number 90 on it was the speed limit on the highway (US90 between Del Rio and San Antonio).

      But walking through that hangar was probably good for controlling the feelings of immortality in the nascent jet jockeys there.

  2. I have been desperately searching my onboard computer for where The WSO went for training in the centrifuge. I want to say Brooks, based on my (admittedly faulty) memory and a Navy website telling centrifuge students when and where to report for centrifuge training. Which is indeed at Brooks.

    One thing I recall is that female flight-suited demi-gods can handle more Gs than the male of the species.

    One last recollection, IIRC it's called the "Hick" maneuver. There are multiple references on line calling it that but I also recall a Nasal Radiator calling it that. On some documentary, somewhere.

    1. I heard the new term in a few video's not in writing, so that spelling makes more sense. Couldn't figure out how they came up with "hook". Anyhow....

      Ras went through the same time I did. He had absolutely no problems with the course. Laughed it off as hard living and high blood pressure.

    2. Lex went for some centrifuge training at PA He had a funny post about a young Ensign in a class to learn the body contortions to ward off GLOC and apparently the enthusiastic Ensign let loose in another area, and thereafter earned a new callsign.

      Your site being a family friendly environment I will leave it to your imagination what that callsign was :-)

    3. I can imagine. DooDoo comes to mind!

    4. Regarding the WSO (specifically and generally), That's got to be especially hard on a back seater. At least for the guy up front, he knows when the stick is going to come backwards and should be able to begin straining in time. Unless crew coordination is exceptional, the back seater may not have a chance to get on top before the O2 reserve in the blood is exhausted and it's nap time. Does she have any comments?

    5. It does surprise you from time to time, but based on what you're doing, you kind of know when to expect the G's...I've been caught unaware a couple of times, and it is not fun having your head in your lap...but not bad enough to GLOC...

    6. Thanks. I appreciate the comment and wish you the best of luck and outcomes in your aviation career. I look forward to meeting your "old man" and you as well.

  3. Reading about your flying and training makes me realize, while I'm a competent Piper driver, I wouldn't last a week in an Air Force training program.

    1. Oh, I don't know about that. While in UPT, after a particularly spectacular (/sarc) ride, my instructor told me "Cheer up, Juvat! Given enough bananas, even a Monkey can be taught to fly!" To this day, I can't stand bananas.

  4. I remember seeing a video of an instructor pilot with a student in an F-16 - they are going into a high G-inducing turn when suddenly you see the student's head in front just bobbing like a rag doll - he was out

    Think there were a number of G-induced accidents in the F-16 until they figured it out.

    Red a post of Lex';s where he is training to fly the Navy's F-16 9F-16N) and he had to go up to PA for centrifuge training.

    Trying to maintain control of a high performance figher while at 7-8Gs - hard to imagine. A lot of grunting?

    1. If you're doing it right, yes. If not, it's usually pretty quiet although sometimes that quiet is interrupted by a loud bang.

  5. For a video on maintaining a Glock, on YouTube:

    Might be less helpful if the wife is in the room, and you may want to wait until you're not at work to watch it.

    No nudity, just lingerie.


Just be polite... that's all I ask. (For Buck)
Can't be nice, go somewhere else...

NOTE: Comments on posts over 5 days old go into moderation, automatically.