T-37 GLOC Syndrome

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So there I was, talking to my watch and relating to my fellow UPT students the exploits of my last solo ride in the mighty T-37B Tweet. I did all the aerobatics, pulled a bunch of Gs, and in all other ways had a blast. Everyone was thoroughly impressed. What I failed to mention to this band of believers was my diving save from busting the bottom of the area. At the end of one of my over-the-top maneuvers, I met the exit parameters but developed a ridiculously down-hill vector pointing out the bottom of the area. No problem. I simply pulled a bunch of Gs at an excessively rapid onset rate to stay in the block. Soon thereafter, my world (previously full of vibrant colors) turned black. You guessed it. I was behind on my G-strain. Well, I released back stick pressure, my vision came back, and I finished my profile. No big deal, right?

I did not really grasp the gravity of this situation until several years had passed and I returned to pilot training as an instructor. I was going through much of the same physiological training I went through as a student with an instructor spin on it. The aerospace physiology lieutenant reminded everyone in the class of the stages one goes through as blood pools in the lower extremities, and oxygen runs from the brain during high G-force maneuvering. Basically, the brain reacts to this loss of oxygen by changing the pilot's vision from full-color to gray (thus, the term "gray-out"). Next, the brain steals away the pilot's peripheral vision and trades it for the infamous tunnel vision. The last adaptation the brain has is reverting to no vision whatsoever, or what we call a "black-out." If this lack of oxygen persists, there is no recourse left for the pilot's brain, so it will slip into the G-Induced Loss of Consciousness (GLOC). 

So why did a rehash of an old aerospace physiology lesson get me concerned about an incident several years in the past? The answer is I didn't really understand how close I was to GLOC-ing that day until I remembered the sequence of symptoms experienced. I basically skipped the preliminary visual cues (loss of color vision, loss of peripheral vision/tunnel vision) and went straight to the "black-out" condition. I was truly fortunate I didn't lose consciousness that day! A quarter of a USAF Photo by Steve Arnold G more, a millisecond quicker onset, a millisecond longer of pulling or any number of hysiological inputs could have pushed me over the ledge of consciousness into the abyss of GLOC--while solo! This was not a comfortable realization. 

It was a realization made more brutal given the dubious distinction the T-37B holds: the airframe with the highest number of GLOC incidents in the entire Air Force inventory. This is nothing new to most readers. But what has surprised me is that the numbers continue to grow with no appreciable decrease in rate. As an assistant flight commander and subsequently a squadron safety representative, I have personally worked four GLOCs in only a year. More astonishing is, as of this writing, there were approximately 300 documented instances of GLOC in the Tweet from 1993 until present (Air Force Safety Automated System [AFSAS]). Three Hundred! And that is only since 1993! This doesn't include incidents prior to the use of the automated tracking system or the undocumented incidents. Have we not learned our lesson? 

To be sure, there are several reasons the T-37B maintains this lofty position. First, it has one of the most rapid G-onset rates of any airframe in the current inventory (the pilot can reach the maximum allowable positive G force of 6.67 in less than one second's time). Second, the pilot wears no G-Suit during flight. Finally, student pilots are the primary flyers of this fully aerobatic jet. 

The first of these factors is an obvious, but uncorrectable problem. The rapidity of G-onset does not allow for much lag time on the Anti-G Straining Maneuver (AGSM), but it has been that way since the beginning. The second factor is also uncorrectable at this stage of the T-37's history, but is not as problematic. Most G-suits only give the pilot an extra one-to-one and a half Gs of tolerance, so not having one should be manageable. The third factor, the student pilot, is the most difficult to manage. 

It is not my intent to harass student pilots with this article, but I highlight their role as primary since all of the above-mentioned instances of GLOC belong to this category (i.e., not instructor pilots). Specifically, this history of GLOCs involves student pilots using an inadequate, incomplete, misapplied or ill-timed AGSM. Only a handful of instances in AFSAS mentioned illness or other such factors as causal, and many of these also mentioned an improper G-Strain as contributory. This is where we should focus on improvement since there are still several years of T-37 flight instruction remaining. 

First, we can improve student performance of the AGSM through training and technique. This does not mean student pilots don't receive adequate training in academics. They do. And they practice the AGSM during their academic phase. But perhaps physiology personnel could perform more evaluations of the students' techniques. Students also receive extra instruction as prescribed by the syllabus early in their flightline training on the importance of the G-Strain. Local units have even instituted a local requirement to fly a "G Warm-up" turn prior to any maneuvering during early blocks of training. But maybe the syllabus has room for more ground pre-briefs, or more G-training (IP flown) earlier in the program. To date, many such recommendations for syllabus changes have been rejected. 

Second, the student must be "ready for the Gs." Given appropriate training, a good strain would have prevented nearly all of the previously-mentioned GLOCs. If, however, the student does not anticipate when to apply this strain, he may soon find himself recovering from a GLOC while dancing to the tune of "The Funky Chicken." The classic example of such ill-preparedness is a pitchout to follow flight lead during formation training, wherein an aggressive turn results in a rapid and high G-onset. While focusing on lead, without recognizing the aft stick forces necessary for the maneuver, the student may neglect his strain causing GLOC. 

Finally, to ensure the success of the AGSM, students must recognize their G-tolerance will change given the day's circumstances. There are a myriad of physiological inputs to this condition, and the student pilot must identify them prior to flight for a successful strain. Will it be hot on today's sortie? Did I get enough sleep last night? Am I stressed out because of my academic test next period? Each of these questions, and more, should be properly answered and the student should know beforehand whether their current AGSM will be adequate or if an earlier, greater strain might be in order. 

Certainly instructors can assist in each of these areas. What the syllabus doesn't mention, the IP can provide. He can provide both instruction and demonstration of G-anticipation (i.e., "Here come the Gs"). Finally, close monitoring of the student's physiological condition prior to and during the sortie can assist in identifying possible G-tolerance complications. In the end however, it comes down to the awareness and discipline of the individual student pilot. 

The GLOC history of the T-37B is well documented and remains a very real problem for its student pilots. Students and instructors should recognize each sortie as having the potential for another occurrence and plan accordingly. With proper training, good G-awareness and an adequate sense of one's own G-tolerance for that day, the student can ensure a solid G-strain for that sortie. Such an approach will prevent GLOCs and keep the student's world focused in vibrant color, instead of pitch black, and allow for more episodes of that ever popular show, "There I Was."