The SR-71 Pilot Full Pressure Suit
David Clark S1030 Suit
Article by Kevin Svetcos, PSD Instructor, Beale AFB, California


The following article is written by Kevin Svetcos, a prior Physiological Support Division Instructor at Beale AFB in California. His job was to inspect and service the David Clark High Altitude Pressure Suits worn by both the SR-71 and U-2 Crewmembers. Additional responsibilities included assisting the crewmembers with the suit-up; functional checks of all systems related to the suits effectiveness; altitude chamber flights and water survival. Above all, these men and women insured that Pilots and RSO's flying the Blackbirds in extremely hostile environments, returned home safely. The job was not taken lightly and this article reflects both the professionalism and dedication the PSD Technicians maintained on a daily basis. In war and peace profound credit is given to these enlisted personnel for their dedication, expertise and professionalism.

They are Patriots in every sense of the word.

Leland Haynes, Webmaster, SR-71 Blackbirds

"The Americans cannot build aeroplanes.

They are very good at refrigerators and razor blades."

- Hermann Goering 

Good thing no one told that to Kelly Johnson and the outstanding people at the Skunk Works.

Then again, maybe they did…

(Lockheed Martin Photo)

Funny thing about Americans. Tell us we can’t do something, and we set out minds to do it. When faced with a challenge, many others will turn away. Those that try and do not succeed early turn away in defeat and look for something a little less formidable that they can handle. Americans, on the other hand, well, let’s just say that we are only getting started at that point. Our eyes get that twinkle. We dust ourselves off, get that smile in the corner of our mouths, and go back at it again. And again. And again. It seems that the greater the challenge, the more we like it. What repels others draws us. We don’t stop until we get what we came for, and we have certainly displayed that in the field of aviation.

For centuries man tried and failed to fly. History’s greatest scientific minds like DiVinci and Galileo were obsessed with the theory of flight and studied it relentlessly. In Greek mythology one can see the fascination with flight and the perils thereof in the story of Icarus and Daedalus. A father and son who were imprisoned on the island of Crete, they sought escape by gluing feathers to their arms. The father, Daedalus, warned Icarus, his son, neither to fly too close to the sun because it would melt the glue and destroy his wings, nor too close to the water because the pinions would be loosened by the moisture. Either one of these extremes would send him crashing him down to his death. Intoxicated by the thrill of flight, Icarus ignored his father’s warning and soared higher and higher until the glue melted, and he tumbled into the ocean and died.

December 17, 1903, the Wright brothers successfully made the first manned, self-propelled aircraft flight, and since then we have never looked back. While we have “…slipped the surly bonds of earth; And danced the skies on laughter-silvered wings…” as Pilot Officer John Gillispie McGee, Jr. of the RCAF so poetically said it during WWII, we will never escape the inherent dangers of returning to the earth once those surly bonds have been slipped. When the first successful airplane was designed, the human performance capabilities were infinitely greater than those of the aircraft’s. That balance has continually shifted as time went on and more and more improvements were made to the airplane, until the time came when the aircraft could finally out-perform the pilot. Although aircrews work hard to maintain excellent physical condition to stave off the effects of flight, every single one has their own threshold of physiological failure. The onset and severity of this failure was of paramount concern to those who flew the SR-71 and U-2/TR-1. At 10,000 feet, onset is virtually unnoticeable and takes a long time to manifest itself to the point of being life-threatening. This allows ample time for recovery and to avoid catastrophe. At 80,000 feet however, physiological failure is instantaneous and fatal. There are some who will read this and think that only the crew of the space shuttle would face a more drastic risk. This is not true. At that altitude, the physiological risk to the shuttle and the Blackbird crews is virtually identical.

The good news was that we have an aircraft that can out-run and out-climb anything in the world. The bad news was that it was so advanced and so dangerous to fly that no pilot could fly it without being killed before the plane even came close to reaching its potential. How can one prove; how can one utilize such a wonderful miracle of aeronautical engineering and national defense if no one could live long enough to reach its limits, forget about living long enough to tell about it? The answer was simple: Get some of those Americans who love to do the impossible; put them in a special flight suit designed to create and maintain a survivable physiological environment; strap that rocket to their butts and send them on their way.

This article will illustrate and put into perspective the SR-71’s advertised capabilities; the reason why its aircrews had to wear space suits and details of what made those space suits work.

Aircraft Performance Perspectives:
The advertised altitude and speed of a typical SR-71 mission was 80,000+ feet (FL800) at Mach 3.2+. In other words, the plane flew over 15 miles above the earth's surface in the stratosphere, which is the second layer of the earth's atmosphere. To bring this height into perspective, say a person were to get into a car and drive in a straight line at 60 mph. for 15 minutes. From the point that they started driving at 60 mph to the end of the 15 minutes time would be the distance between sea level and the belly of the plane.
Think about this the next time you get on an airplane: commercial aircraft normally cruise at about 35'000 ft. (FL350). Almost everyone has ridden on an airplane and looked out at the ground from the window at one point during the flight. If the SR and the commercial liner were flying intersecting courses and both were at their respective advertised cruise altitudes, the SR would be as high above the commercial liner as the commercial liner was above the ground, plus another 10,000 f eet.

The speed of sound, or "mach" is 769.7 mph. At an advertised speed of mach 3.2+, that would be over 2,463.3 mph. How fast is that? Look at this example: the circumference of the earth at its equator is 24,901.55 miles. With all things being equal and all participants of this example already at speed (i.e., no refueling or drag coefficients to slow any of the subjects down), the time it would take to go all the way around the world would be:

SR-71:  10.1 hrs

30.06 rifle round: 13.5 hrs.

AK-47 rifle round: 15.2 hrs.

"Tomahawk" cruise missile:45.3 hrs.; and for the curious,

The average space shuttle: 1.4 hrs.

Physiological Hazards of Flight: Of all the dangers involved with flying,  hypoxia, or the decrease of oxygen in a person’s blood system is the greatest. Theoretically speaking, hypoxia is simply another form of suffocation induced by a decrease in barometric pressure (increase in altitude). To fully explain the theory of atmospheric pressure changes would require a more lengthy discussion best suited for another section other than this page. Therefore, at this point we will simply say that the higher the altitude, the higher the danger, and the lower the body’s ability to process oxygen. 

The most common form of hypoxia, hypoxic hypoxia, is caused by a reduction of oxygen pressure in the lungs or exposure to altitude. Another form of hypoxia, stagnant hypoxia, is caused by poor circulation of blood flow, which in turn results in the pooling of blood in any part of the body; normally the head, feet, or abdominal cavity. The most obvious manifestation of this is G-LOC, or loss of consciousness due to excessive G-forces experienced during high-speed aircraft maneuvering. Positive G’s occur when any maneuver forces blood towards the aviator’s feet, therefore reducing the blood flow to the brain. Negative G’s are just the opposite, where too much blood is forced towards the head. Transverse G’s, while still a very real threat, are the easiest to cope with as the pressure experienced forces the blood and internal organs either backward or forward in the abdominal cavity. The one cause of stagnant hypoxia that people rarely, if ever, are even aware of is from sitting in one position for an extended period of time. The next time you get up from sitting in class, sitting in a meeting, at your desk or in your car, and you notice that loss of feeling in your legs, muscle tightness, and you start stretching, yawning and have a sudden desire to take a nap, that is the result of stagnant hypoxia.

To illustrate the significance of the altitude at which the SR-71 operated, the everyday hazards that the fliers onboard faced and the absolute necessity for a full pressure suit, look at the physiological phenomenon known as "Armstrong's Line". Armstrong's Line is the barometric pressure level where gas begins to escape from liquid (boil) without heat, which is 60'000 ft (FL600). In high school, we learned that the human body is about 70% water. If a human being were to be exposed to the atmospheric pressure found at this altitude, they would be unconscious within 8-10 seconds and dead within 15. At the SR's advertised operational altitude of FL800, that same person would be unconscious in 3-5 seconds, and dead in less than 10.

Except for an external oxygen and supply, the pressure suit itself was a completely self-contained, controlled environment. It is designed to protect the wearer from the physiological dangers of high altitude, to keep him comfortable in the harsh environment and to act as part of the flier's survival gear should they land in a cold environment or in water. At the very beginning of NASA's Space Shuttle program, the Physiological Support Division at Beale loaned out several of its full pressure suits to NASA for the shuttle crews to fly in until the shuttle's triple pressurization safety system s was checked and verified for proper function. If one compares pictures of the early shuttle crews and the later shuttle crews, they will see that the early crews wearing the golden S1030 full pressure suit and the latter wearing the darker orange suits.

The SR-71 crews wore David Clark S1030 full pressure suits and helmets, while the U-2/TR-1 aircrews wore David Clark S1031s. There were four basic components of the entire ensemble: the helmet, a pair of gloves, the torso harness, and the suit itself. While the suits were almost identical one to the other, there were some very subtle, yet significant differences that will be identified later on.

Author, Kevin Svetcos testing the David Clark Pressure Suit

(Crickmore Photo)

The Suit: 

A fully enclosed suit with a double zippered rear entry, it had enclosed feet at the bottom of the legs, full-length sleeves with metallic rings and a locking mechanism that acted as a connecting point for the gloves. The head opening had another metallic ring with a locking mechanism that served as a connecting point for the helmet. The second component was the helmet, the third were the gloves and the final component was the torso harness, which was part of the egress and survival systems that was worn over the suit itself. Standard flight boots were worn with the ensemble, the only difference being that the boots were a full 2 – 2.5 sizes larger to accommodate the feet of the suit when inflated.


There were four basic layers to the suit itself.

They are described here starting from the inside out: 

1) Comfort Liner: This was a lightweight green nylon liner. The vent tree of the suit (to be discussed later) was snapped to the outside of this layer. During the donning of the suit, the comfort liner helped the ACMs because it was smooth and slippery, and the cotton underwear they wore slid across it as if it were Teflon. During the flight, it also absorbed and distributed the sweat from the fliers when their underwear became saturated, which happened on almost every single flight. Another purpose of the comfort liner was to add a smooth layer between the pilot and his environmental systems like the incoming ventilation and distribution system, the suit’s pressure regulator, and various glue sites and tape where different pieces of the suit were married together.

It also made it easier for the fliers to move around in the cockpit because the suit was so big they had  little extra room in the suit. When they inflated the suit a little bit, they could shift around in their positions without the suit actually moving that much if at all. Velcro attached the comfort liner to the second layer around the opening for the neck ring, glove rings, at the seam point of the “booties” and legs just above the ankles, and all along the main zipper opening.

 2) Bladder/Thermal layer:

    The second layer of the suit served a dual purpose. Not only was it the main bladder that actually inflated and held the pressure for the suit, but it was also a thermal liner. The bladder consisted of two separate layers of non-porous material. The material was sealed together at literally thousands of places by little circles that looked very much like a quilt when inflated. The purpose of the thermal layer was so that in the event of egress into a cold environment and/or into water, it could be inflated. In addition to adding a minor amount of added buoyancy if in water, the added layer of warm air could give the ACM another 45 minutes over not having it inflated. They had a small black inflation hose stored in the top right thigh pocket of the outer cover of their suit that was connected to the bladder, which had a spring-loaded, rubber-tipped valve. The valve was clipped and taped in the open position to allow for the expansion and compression of the air in the layer as the plane passed through the various levels of flight. As the altitude increases, the ambient air pressure decreases. That means that any trapped gases or air inside something (balloon, bladder, ear drums, sinuses, etc.) will expand, or get bigger. By taping the valve open, the expanding air escaped from the thermal liner as the cabin pressure decreased. If the flier needed to inflate the layer, he would remove the tape and clip, push against the valve with his teeth and blow into the hose. When they took their mouths off the valve, it sprang shut. When it was inflated, the clip would be re-applied with the valve in the closed position to ensure that it was not accidentally opened and the air allowed to escape. The bladder was also the layer that was incorporated with the zipper, the neck ring, glove rings and booties of the suit, pressure regulator and ventilation inlet.

3) Outer mesh: The outer mesh played a major role in the overall construction of the suit. It was made out of a fishnet material and design, and it is the piece that makes it so that the suit maintains its original shape and form when inflated. With the mesh cover, the suit will maintain the basic characteristics of a torso, arms and legs and will assist in the distribution of pressure throughout the bladder to avoid strain on any one part. Without the mesh, the suit would more closely resemble a big ball for the body, with smaller balls attached to it for the arms and legs. The mesh also had several areas on the arms, legs and waist area that were adjustable with cords. These areas allowed custom fitting of the suits by allowing material to be taken up or let out to fit the flier's specific physical build.

4) Outer Cover:

      The final layer was the outer cover. Made up of flame resistant and tear resistant yellow Nomex material, this cover went over the entire assembly. It zipped to the neck and glove ring areas, and attached to the main opening, UCD assembly, regulator and vent ports with Velcro. It had the same type of pockets in the same locations as a standard flight suit to include patches of female Velcro that the flyers could attach various things to. On the upper left arm where the pen pocket was, the fliers kept an extra feeding port probe, as well as a rubber stopper that was there in case the food port flap going into the helmet didn't close or seat proper and allowed for leakage. Both sleeves had a flap that folded down over the glove ring assemblies to protect the glove rings from any potential damage or from becoming accidentally unlocked if hit against something. On the left sleeve there was sewn a checklist for egress from the aircraft, and on the right sleeve there was sewn a parachute descent checklist of things to do once out of the aircraft following a successful egress.

The Helmet:

Like the suit itself, the helmet used in this configuration was made up of different parts.The outer shell was made of fiberglass and shaped more like an oval than a circle, although the difference was barely distinguishable. This outer shell was integrated with a metal ring that locked into the neck ring of the suit using “dogs”, or a series of over 80 separate spring-loaded latches that locked into place once the helmet was fully seated into the neck ring. There was no stop point on the rotation of the helmet, so theoretically speaking; it could spin freely 360 degrees clockwise or counterclockwise. 

There were two different and very distinct sections of the helmet. The primary section was the front where the flier's face was, which was sealed tight from the back portion of the helmet by a snug neoprene face seal. There was a large opening in the front of the helmet's shell that allowed an unrestricted view for the flier. All around the opening was a small gray rubber strip that had over 100 little holes in it, each hole being the size of the head of a pin. This is where the oxygen flowed into the face cavity.  Instead of blowing directly into the face, it flowed across the “clear” face shield, partly to keep from going directly into the wearer’s eyes, but also to assist in the defogging of the face shield from the warm, humid breath of the ACMs. The word “clear” is in quotes because the face shield really wasn’t. In reality, they either had a minute layer of gold over the glass, or there were numerous wires that ran horizontally all the way across and made up the final part of the face heat system for the helmet. To tell which was which, all one had to do was to hold the visor up to the light and look through.  If a series of hairline squiggles spaced about 1/16” apart didn’t run across the front of the face shield, then the faintest golden hue could be noticed. Gold was used for the face heat system because of its ability to conduct heat at a low temperature. The visors needed to be warm enough to defrost and keep them from fogging up while at the same time not make the ACM sweat.

Yes, it was real gold.

The face shield had a small electrical wire that ran over to the communications port and was integrated with the communications system for the helmet from the inside. The outer/second visor on the helmet was the sunshield, and it was a dark green. This was nothing more than one great big sunglass lens, almost as dark as the shade on a welder’s mask.

While the sun visor was a simple visor raised and lowered by hand and could be left at any position between full open or full closed, the face shield was another matter. The face shield was connected to a locking mechanism called the Bailer bar. The face shield could be either full open or full closed, but to lock and secure it, the Bailer bar had to be brought all the way down and secured to a small latch directly in the middle and just below the face opening in a hook-like fashion and a safety lock fully engaged by pushing another lever all the way down. One knew both were properly engaged when they either heard or felt both of these mechanisms “snap” into place and the visor could not be opened when the Baylor bar tugged upon. At the pivot point of the Bailer bar was a small white Teflon pin on the helmet’s left side that was relaxed in the visor’s open position and depressed when the bar was down and locked. This was crucial because that single pin was what either engaged or disengaged the oxygen regulators and either started or stopped the flow of oxygen to the face cavity. (Lockheed Martin Photo)

NOTE: This is where the SR’s S1030 and the U-2/TR-1's S1031 helmets differed. Where the S1030 had the on/off capability, the S1031 had a continuous flow regardless of face shield position. This was in response to the difference in aircraft performance. Regardless of aircraft, the ACMs had to pre-breathe 100% oxygen for at least ½ hour prior to reaching their mission’s altitude. The SR-71 had to meet up and top off its tanks from a refueling tanker prior to ascending. This took the better part of 30 minutes, so they didn’t have to lock their visors down until just prior to the safety pins being pulled from their egress systems.

The U-2 was a different animal, though. It did not refuel therefore it climbed straight away. This difference was even more obvious to those who were privileged enough to watch the launches, and witness her literally stand on her tail before she got 2/3 of the way down the runway. This meant that the pilot went on oxygen right when the pre-flight tests were begun and a continuous flow of oxygen was required.

On the left side of the helmet just below the face opening was a round knob used to adjust the helmet’s microphone, once the visor was closed. Keep in mind that once the visor was closed, the fliers began “pre-breathe” (purging of nitrogen from their system), and they were not allowed to open up again until their descent below 10’000 ft. at the end of their mission without having to start the pre-breathe period all over again. If that visor was accidentally popped and oxygen integrity compromised, it was back to the very beginning.

On the right side of the helmet and about 1 ½” of center was the feeding port. This was an opening with a spring-loaded flap about the size of a large straw that the pilots could stick the tubes in order for them to drink, or eat "tube food", without introducing a leak. Tube food was food which was food in a paste form and packed into an aluminum tube the same shape and size as a standard tube of toothpaste. Fliers had their choice of beef and gravy, butterscotch pudding, applesauce and peaches, to name a few. If for some reason the spring mechanism were to fail, there was a small round rubber stopper in the sleeve pocket that they could press into the feeding port to prevent loss of pressure from their helmet. Behind the feeding port were two small test ports in the helmet. One led to the face cavity and the other into the suit portion of the suit, intended solely for taking the required pressure and flow testing measurements. When in storage, the male probes used for testing were replaced by screw plugs that were secured tightly into the holes.

Back on the left outside part of the helmet shell was what looked like a black disc about two inches aft of the microphone adjustment. This was the cover to the anti-suffocation device, or “anti-suff valve”, and this device was the only way that ambient (outside) air was to be introduced into the suit as a survival measure. A thin, Teflon wafer about 1 ¼” inch in diameter and held against the opening in the helmet, this device was designed so that if the flier lost their oxygen supply such as in the case of egress, then if they were to inhale hard enough, the spring would compress and allow air into the face cavity. The driving scenario behind this was water survival where a flier had to keep their face shield closed and locked to avoid water getting in and filling their suits, which would ultimately result in dragging them down to the bottom and drowning them. With the visor closed and the anti-suffocation cover designed in the manner that it was, while some water was certain to get in, it would be a miniscule amount, greatly reducing the risk. Resistance for the anti-suff was set so that even if unconscious, air could be drawn in to avoid suffocating the flier. Further back on the left, just behind and below the left ear was the communications port that the internal communications and face heat wiring ran out of to connect to the aircraft’s systems.

The next component on the right side of the helmet towards the back and right about horizontal center of the head was what was called a take up reel. This reel was a device that was attached to a spool that a string was wound around, which was in turn attached to several points of the neoprene face seal and laced through several eyelets on the inside of the helmet. This system was used to draw the face seal snugly against the face to prevent any type of leakage between the two cavities of the helmet. At the end of the flight, the reel was relaxed and the seal loosened to allow removal of the helmet. In the very back and dead center was attached the two oxygen hoses that connected the suit’s oxygen system to the plane’s oxygen supply via the seat kit. The hoses fed into the helmet’s regulator, which will be discussed later.

On the inside of the helmet and on the inside of the face cavity, the face seal was attached to a bigger, looser drape-like piece of airtight material that was glued around the entire inner opening of the face opening. To the left of the pilot’s mouth was the mike, which as described earlier was roughly adjusted before closing up for testing and pre-breathe, then adjusted from the outside by the knob. Further back and on the same side as the opening for the anti-suff, and to the right was the opening for the feeding port. Right about even with the flier’s mouth and integrated into the larger drape-like piece of the face seal was an exhalation, or “ex” valve. This valve worked on the same basic principle as the anti-suff. The ex valve was a clear plastic disc that was held in place with a spring and tri-valve. Pressure from the suit and the spring kept the valve closed, but as the flier exhaled, the force of the exhalations was stronger than the spring. This is how oxygen was circulated through the face cavity. Theoretically speaking, if given enough time the ACs could inflate their suits by breathing alone.

The part of the helmet in back of the face cavity was part of the overall full pressure suit itself. While the face cavity was maintained at roughly a 1:1 pressure ratio, or effort equal to breathing at ground level, the back part of the helmet and the suit itself even at full inflation still experienced the atmospheric pressure of about 32,000 ft, or FL320. Although maintaining the body at a safe atmospheric pressure, without the aid of 100% oxygen, this altitude is still lethal if exposed to for a long enough period of time.  Inside the helmet was a liner made of a firm sponge foam material that contained earphones for the communications systems, covered in nylon with a communications wire connected to another wire in the helmet, which in turn was integrated to the plug that was attached to the plane’s main systems. The helmet liner was secured to the top of the shell of the helmet by a piece of Velcro about 3 ½” in diameter. If the two pieces of Velcro from the helmet and the liner did not match exactly, it could cause a hot spot, or a point on the flier’s head that after a while could feel like someone was pressing down hard on top of their heads with a finger. While only annoying at first, after a couple of hours, it could become very painful.

The final part of the helmet was the dual oxygen regulator attached to the inside of the helmet. Fed by the oxygen hoses attached to the plane’s main system, it had two regulators side-by-side, each one an independently functioning barometric aneroid. A barometric aneroid is something that detects differences in atmospheric pressures, then automatically adjusts those pressures to meet the acceptable, predetermined levels. There were two sections separated by a flexible rubber diaphragm. As the ACs breathed in, oxygen flowed into the face cavity by way of the gray spray bar mentioned at the beginning of this section. As the pressure in the supply tubing that ran from the regulators to the spray bars decreased, the regulators sensed the pressure difference and opened up, allowing oxygen to flow from the plane to the pilot. When the inhalations stopped, the pressure equalized and the diaphragms closed. During exhalations, the exit pressure was greater than the entrance pressure, so no oxygen was allowed to flow. In addition to allowing oxygen to flow to the spray bar, the regulators ensured that regardless of the pressure coming from the plane’s system, only a certain and constant level of pressure would be sent through the helmet’s delivery system.

The Gloves:

While not as complex as the suit or helmet, the gloves were equally vital to the overall survival of the fliers. There were three main components to the gloves: the bladder, the cover, and the glove ring. The bladder was a heavy-duty rubber glove much like one of the rubber gloves one would find for doing cleaning, like the Playtex Living Gloves. It had small tabs at the top of each finger that allowed them to be stitched to other small tabs on the inside of the fingers in the cover to avoid twisting and ease in the donning and doffing of the gloves, and a rubber flange around the opening to allow integration of the cover, bladder and glove ring hardware. The glove cover had the same Nomex material on the back of the hand that was used for the outer cover of the suit, but had black suede leather palms. There were also two straps that ran across the back of the hand that were tightened to maintain shape of the glove to avoid it blowing up like a big balloon.

The hardware consisted of a ring at the bottom that integrated fully into the sleeve of the suit, and like the helmet, allowed for unrestrained movement for a 360+ degree range of rotation. The bladder was integrated to the inside of the glove ring by cloth tape and glue, which not only made an airtight seal, but also was very, very strong. A small ring that screwed into the connecting hardware and sandwiched the cover and bladder in between connected the entire assembly.

The Torso Harness:

The torso harness was designed primarily for egress and survival. Made of Nomex material, it was basically just a cover for the torso portion of the suit. Zippered in front, it had no sleeves or legs. The assembly contained:

The water wings were a dual-celled heavy, non-porous nylon cloth with manual valves to allow inflation or deflation.  During maintenance inspections, a vacuum was applied to the inner cell to deflate it as much as possible to reduce its size and remove any air that may be trapped in it. The valve was clipped in the closed position to prevent air from entering into the cell once all air had been removed. The exterior cell was squeezed by hand to get it to the size needed to roll it up small enough to fold and replace into its pocket.  This valve was clipped open to allow the escape of trapped gasses during flight and prevent partial inflation when exposed to the lack of atmospheric pressure in the cabin. They could be inflated either manually by pulling a tab underneath, which activated a compressed carbon dioxide charge, or by a hydrometric (water sensitive) aneroid. The wings were compressed and rolled up tightly,  then stowed in large pockets around the back and chest of the torso harness, then secured by Velcro closures. The wings were designed so that when in the water, they would keep the flier's heads up about 8-10" above the water and orient them in a face-up position. This would keep their heads out of the water in case they were unconscious and avoided bringing in water to the face cavity via the anti-suff valve described previously in the helmet section.

The Hardware:

The most important part of this entire system was the pressurization system that fed off of the aircraft and into the flier's suit. Not only did it inflate the suit, but cooled it as well. There was a ventilation hose that was attached from the aircraft to the suit. The fliers could adjust the amount of airflow into the suit by adjusting a device called a "T-block", which was the actual vent hose/suit integrator.

The T-block in turn was connected by a locking ring to the inlet of the suit through which air passed by a device called the flapper valve, which was just below the floatation device on the left side of the suit. The flapper valve was a ridged, round rubber disc oriented so that it would allow air in but not out of the suit, held in place and protected to an extent by a round metal disc with many, many holes in it to allow the flow of air. This in turn led to the vent block that distributed the air throughout the suit. Made up of 3 tubes using a spring-like design and encased in loose mesh and nylon, the incoming air was taken throughout the entire suit via these tubes. Called the vent tree, it looked like a big black spider when disconnected from the comfort liner and hanging out of the suit. There was a vent that ran up to feed the suit portion of the helmet, one each that ran the entire length of each sleeve and was tucked into the back of the glove during the suit donning process, one each that ran down the side of each leg s almost to the ankles, as well as two branches that wrapped partially around the to the back of the flier. 

The most crucial item to this system was the suit pressure regulator. About the diameter of a softball and weighing close to a pound by itself, this component had a triple pressurization system.  It was screwed into a reinforced opening of the suit just below the ribs and held in place by a locking ring just below the floatation device on the right front side of the suit. The purpose of the regulator was to control the release of air from the suit, and during missions it was common practice for the ACMs to inflate the suit a little bit in order to take some of the weight of the suit off of them. Depending upon which one of the regulator's system was being used, the suit would hold absolutely no pressure, or it would be so full that one could not even dent the suit should they grab with both hands and squeeze.

The main system for the regulator was a barometric (pressure or altitude sensitive) aneroid that would open and close in accordance with the atmospheric pressure that it was exposed to. This system was designed so that when it detected a drop in the cabin atmospheric pressure, the internal valve would close and trap air in the suit until an equal pressure was achieved and maintained. The suit could inflate to the point where it gain a little size, or it could inflate to its full capacity depending upon the situation. The biggest asset of this system was that it could instantly inflate to its maximum capacity, which was an absolute must in the event of a rapid decompression or egress. The first manual system for suit inflation was called the "primary" system. This consisted of a round knurled knob that could be twisted to adjust pressure retention in the suit, very much like how a rheostat, or dimmer switch, controls the brightness of a light. Obviously, this was the most desirable system to use. In case the primary system did not function as intended when needed, then there was a back-up or "secondary" system. This was composed of a simple push button that would totally close off the release valves in the regulator and inflate the suit. The asset of this system is that it would fully inflate the suit almost immediately. The liability is that to maintain the pressure, the flier had to keep his finger on the button, and it was an all-or-nothing pressurization. The problem of keeping the finger on the button was further complicated by the incredible pressure inside the suit and the difficulty of mobility while inflated. 

Another important piece of equipment was the helmet hold down assembly. This was a strap and pulley system that connected between a cable that attached to the neck ring and a piece of hardware that was connected to the top of the zipper opening in the groin area of the suit. The strap was loose during donning, doffing and when the pilot was mobile, but during testing and cockpit integration, the take up was tightened so the slack was taken up. This was done so that when pressure was applied to the suit, it would not do what it would naturally be inclined to do and straighten out. Instead, it would keep the ACMs head tucked forward and not flying back against the seat. It also drastically reduced the potential for injuries to the head and face from the force incurred during the inflation of the suit from a rapid decompression.

The final piece of additional hardware on the suit was the UCD, or Urine Collection Device. Due to the duration of the missions and the fact that the fliers could not move about freely as was allowed by the transport, bombers and other large aircraft, there was a need for a way for the ACMs to relieve themselves during the mission should the need arise. The answer to this is the UCD, a soft rubber piece that the flier wore on his person. It was fitted through and secured to his undergarments with Velcro. At the end of this portion of the UCD was a clip that was secured to a tube that was located in the left leg of the pressure suit, and then wrapped with tape to ensure that the connection was not compromised once the suit was put on. This tube then attached to the UCD valve on the inside left thigh of the suit. When the ACM wanted to relieve himself, he would first slightly increase the pressure in his suit by adjusting the primary system on the suit regulator. When the suit was inflated to an acceptable pressure, the UCD valve was pressed down, which created a flow of air out of the suit and into the main area of the urine collection device. The air flow was required to flush the urine through the system away from the flier, out of the tubing and hardware, and into the actual collection device. Upon completion, the UCD valve was closed and the suit pressure backed off.

NOTE: This is where the second major difference between the S1030 and S1031 is evident. Everything up to the UCD valve is identical in the two suits, but with the S1030 worn by the SR-71 crews, there was an internal tube that led to a "piddle pack" that was snapped to and wrapped around the lower portion of the leg on the inside of the Nomex suit cover. This was a basically a bag with several small, dry and compressed sponges that absorbed the liquid as it was introduced. There were some very rare occasions where the bag was filled past capacity, but not very often.

With the S1031 suit worn by the pilots of the U-2/TR-1, they had an external rubber hose that was inserted into a fitting at the bottom of the control yolk and emptied into a container under the floorboard of the aircraft.

(The way that I was able to remember the difference between the suits was the same way I taught my trainees: Remember that of the two suits, there was only one with a piddle pack attached, and one without. We used the last number in the suit's nomenclature to remember that the S1031 was the "1" without. Odd, but effective.)

There were other smaller standard things in the suits such as the hook blade knife in a leg pocket and secured by some parachute cord, a signal mirror, small compass, a self-doffing lanyard used to help the ACMs get out of their suits by themselves if required, and whatever personal items they carried.

As one reads through the above description of the full pressure suit, its components and their functions, they might notice a fair level of redundancy. There were two oxygen hoses that fed the regulators for the helmet, which was a dual system. Two zippers were used in the suit closure, there were two separate cells for the flotation devices, and there were three different systems in the suit’s regulator to inflate the suit. One of each of these items was sufficient to perform the tasks required of them. The additional back-ups were added in the event of failure of the primary system for insurance, although the author has no knowledge of any situations where the primaries failed and the back-up systems had to be utilized.

SR-71 Crew Major's Danielson and Gudmundson

(Crickmore Photo)

Out of literally thousands of applicants that the programs reviewed every year, only a handful were chosen to be interviewed, and even fewer made it through the entire process to become aircrews of the SR-71, the highest and fastest flying aircraft in the world. It is common knowledge that they put themselves in harm's way from heavily guarded ground-based defenses and overt aggression on behalf of countless enemies. What many people don't realize is that whenever they flew the airplane, whether it be operational or training missions, over foreign, international or domestic soil, their lives were in constant danger from the very environment itself. The nature of their missions and their reason for even existing in the first place was stressful enough for them without having to worry about the dangers. The ground crews that cared for the planes had great pride of ownership and were absolutely meticulous in their care. The men and women of the Physiological Support Division made this commitment to all air crews that flew these suits: we promise that once you leave the ground, you will return to it safely – with or without the airplane.

(Lockheed Martin Photo)

As you have seen, full pressure suits have served, unwaveringly and with honor for many years not only Air Force fliers, but the astronauts of NASA's space shuttle program and High Altitude Missions Branch as well. They have safeguarded the ones who in turn have helped safeguard not only the security of the United States, but the ideology and freedom throughout the world. With nothing more than the speed and altitude of the aircraft as their only defense, these crews flew into situations that required intense concentration, flawless execution and the ability to remain calm even as they looked out their canopies at the occasional rocket or missile who's sole purpose was to end their lives. One of the last things they needed to worry about was if their suit s would work. The purpose of the suit was to keep the crews alive under any situation inside or out of the airplane. The purpose of the people who maintained the suits was to make the suits operate so efficiently that the ACMs couldn't tell if they were standing still on the ground or flying at speed and altitude; to make them forget as much as possible that they were wearing this 40+ lb. plastic bag and helmet, and the gravity of the situation that necessitated its use in the first place so that they could focus on the task at hand.

SR-71 Crew Major's Bledsoe and Blackwell

Pressure suits have been around for a long time in some form or another, protecting those who protect us. This article is dedicated to those whose job it was to make sure that whoever left home, came home.

Kevin Svetcos, Author

(Lockheed Martin Photo)

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First Created: April 15, 1996 - Last Revised: March 29, 2004
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Article and Photo Credit:
Author of this article: Kevin Svetcos, Beale AFB Physiological Support Division Instructor. This article is copyrighted on May 31, 2001 by Kevin Svetcos. All rights reserved. Date of last revision is July 09, 2001. For corrections or inquiry Email Kevin at:

Osprey Photos (Used by permission) are the Copyrighted property of Paul Crickmore, Author "Lockheed SR-71, The Secret Missions Exposed". Additional photos are copyrighted by the Lockheed Martin Corporation, NASA and the Auburn Files.

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Revised July 09, 2001

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