Fighter pilots can black out in seconds during high-G flying. Here's how flight experts say they train to stay conscious.

• Air Force pilots are extensively trained to prevent loss of consciousness during high-acceleration flights.
• The Anti-G Straining Maneuver helps pilots maintain consciousness when they fly.

You're flying a fighter aircraft, and you are accelerating. But you're relaxed — a little too relaxed. Suddenly, you notice your peripheral vision beginning to fade. In what may be just seconds, you completely lose consciousness.

That's G-LOC, or G-induced loss of consciousness, and the results can be catastrophic.

In flight, levels of acceleration known as G-force vary, and when pilots experience its highest levels, the pressure of gravity pushes blood to the lower half of the human body, causing low blood circulation in the upper half of the body.

"When that happens for an extended enough period of time, you will lose consciousness," Lt. Col. Carolyn Price Moore, an aerospace physiologist and the chief of the 19th Air Force's Aircrew Performance Branch, told Business Insider.

Air Force pilots must prepare their bodies for the reaction at the highest levels of acceleration during their flights. Experts broke down how pilots make it through these high-pressure endeavors.

"All the training that we do, the goal is to ensure that the pilot is capable of doing the maneuver," Price Moore said.

The Anti-G Straining Maneuver, also known as AGSM, is an exercise pilots use during high levels of G-force to prevent G-LOC.

Air Force pilots are taught about G-forces, AGSM, and all the ways that increased altitude and pressure can affect the body as early as their first week of training in the classroom.

Learning the ropes

When pilots are just starting out, their introduction to G-force is gradual. This gives them time to build the physical fitness to withstand pulling Gs.

"You really just want your lower body to be very strong, so if you can do working out that improves your lower body strength that's gonna go a long way towards helping with G tolerance," Price Moore said.

Athletes tend to have an advantage when it comes to preparing for high-G-force flights as they may already have significant lower body strength. Although height is beyond the pilot's control, it also helps to have a short stature as blood can circulate in the body faster.

Students are put through an introductory primary acceleration training where they are individually spun in a human centrifuge that gradually increases in Gs.

"It's a nice slight, just kind of slow climb up into the G realm that lets them kind of get used to the feel of the centrifuge," said Senior Master Sgt. Tyler Long, who has overseen training performance facilities.

He called the training a "roller coaster on steroids," saying "it's a feeling you've never felt before in your life."

Students wear G-suits that act as an external "air bladder," squeezing the lower body to promote blood flow if a student doesn't have enough lower body strength to flex on their own.

Training also includes what Long describes as the SACM (Simulated Aerial Combat Maneuvers) profile, a simulation in which the student has to track an aircraft onscreen while they undergo and ride out varying levels of G-force.

"The whole point is proficiency. Get them proficient with this G strength, get them comfortable to a point where they can now go and fly a higher G capable aircraft," he said.

New Air Force student pilots start out flying a T-6 Texan II aircraft, within about seven months in Undergraduate Pilot Training and move forward to either mobility or heavy aircraft training using the Air Mobility Fundamentals-Simulator or fighter and bomber training in a T-38 Talon aircraft. Students are assigned an aircraft by the end of UPT. The student will use this simulator for several months.

An undergraduate pilot will then move to fly a T-6 Texan II aircraft within about seven months in Undergraduate Pilot Training and move forward to either mobility or heavy aircraft training using the AMF-Simulator or fighter and bomber training in a T-38 Talon aircraft. Students are assigned an aircraft by the end of UPT.

Once the student masters this training they will fly the aircraft they were assigned and master it during the Formal Training Unit.

Handling the real thing

The two main mechanisms of AGSM that prevent a pilot from passing out are calculated breathing and the squeezing of the lower body. It's a simple but life-saving maneuver.

Before the pilot even enters G-force onset while flying, they have to flex their lower body like their glutes, hamstrings and other muscles as tight as they can.

"They just tighten and hold and what that does is it actually compresses all of the blood vessels, all your veins and arteries in the lower half of your body to help prevent that pooling," Price Moore said, explaining that the flexing allows the blood to stay and continue circulating the upper body.

The more challenging step is executing the proper breathing technique. This allows blood flow to return to the heart and then to the brain.

A pilot should take a big deep breath, holding the air in their glottis, which is located in the throat, before the G-onset or acceleration occurs and then they begin the "air exchange."

The air exchange is the quick release of air that should occur every three seconds. "It's not a normal breath, it's a forced air exchange where you are essentially forcing the glottis open and closed really, really rapidly," Price Moore described.

The sound of an air exchange sounds hoarse, like a mix between a gasp and a cough.

In training, this is all done under the supervision of the instructor who is accompanying the student in the aircraft. They must listen for the air exchanges to ensure and approve whether the pilot is breathing correctly.

Accidents still happen

Sometimes G-induced loss of consciousness cannot be avoided and a pilot might also experience symptoms such as brief amnesia, nausea, disorientation, and confusion, as well as neck and back injuries.

Flight accidents have also occurred as a result of pilots passing out. For instance, among other incidents, both the Navy Blue Angels and Air Force Thunderbirds have lost demonstration pilots to G-LOC.But many military aircraft are now equipped with an Automatic Ground Collision Avoidance System that help to prevent accidents from happening.

"When the auto GCAS is engaged, the aircraft itself gets texts if it is essentially too close to the ground, and if so, the aircraft itself will take over and do what's called a 'fly up,' and we'll fly the aircraft back up to a safe altitude," Price Moore explained.

"Since the installation of auto GCAS we have had far fewer incidents of G-induced loss of consciousness mishaps or accidents," she said, adding that "operationally, the auto GCAS has kind of been a game-changer in terms of G-LOC mishaps, so there's that guardrail."

But even with a kind of safety net in the aircraft, that doesn't make it any less necessary for US military pilots to train as if they don't and ready their bodies for the intense high-pressure challenges of high-G flying.

Correction: April 29, 2024 — An earlier version of this story misidentified a training aircraft and simulation profile. The Air Force uses the T-6 Texan II in initial training and the SACM (Simulated Aerial Combat Maneuvers) profile.