Deadly Disorientation
Vertigo simulator teaches the dangers of spatial disorientation

by Mike DiFrisco

I was cruising along at 5,000 feet MSL on an overcast day when I bumbled into the solid deck of clouds. Just then, Center asked me to ident. I momentarily tipped my head to glance at the lower panel where the transponder was located-and my brain exploded in a swirl of dizziness. I felt the airplane’s right wing drop sharply. In panic mode I corrected with a jerky turn to the left. But with no outside horizon to guide me I had no idea if my wings were level.

With my heart in my throat I finally looked at my instruments that verified, contrary to my inner ear, that I was now in a steep left turn. I corrected to the right and settled into straight and level flight. I composed myself, pitched down, reduced power, and popped out of the clouds into clear skies over EAA AirVenture Oshkosh 2001.

Stupid pilot trick? Yup. Good thing I was flying the FAA’s portable spatial disorientation simulator, which is secure in the FAA pavilion and not a real airplane in real weather. Experiencing the physical and emotional upset of vertigo was an important lesson, one intended to motivate pilots not to push from VFR weather into instrument meteorological conditions. And it’s a lesson any pilot can take at EAA AirVenture in the FAA’s Vertigon, its gyro-based vertigo simulator that graphically demonstrates the dangers of spatial disorientation.

Spatial D
Spatial disorientation is defined as "a state characterized by an erroneous sense of one’s position and motion relative to the plane of the Earth’s surface."

In simple terms, spatial disorientation is caused by the senses of the body misrepresenting the pilot’s position in space. Three systems make up the body’s orientation senses:

• Vision (your eyes)
• Vestibular (your inner ear)
• Proprioceptors, or the somatosensory system (the "seat of the pants")

These sensory systems work in concert when flying, but vision is the most important sense because it accounts for roughly 90 percent of our orientation. The eyes send pictures to the brain that keep us clued in to the airplane’s position, velocity, and attitude relative to the ground. The better the pictures, the better our orientation.

Keeping everything right side up on a clear VFR day is easy because we see good pictures. At night and in poor visibility, like instrument meteorological conditions (IMC), what we see isn’t distinct and clear, and we humans are prone to spatial disorientation when we are denied normal and expected visual cues.

Why? Because the vestibular system (with some "help" from the seat of the pants) takes over and provides the orientation information the eyes can no longer provide. The primary component of the vestibular system is the semicircular fluid-filled canals in the inner ear. Think of them as biological accelerometers that sense and transmit changes in pitch, roll, yaw, and velocity to the brain.

If the brain is denied the visual images that allow it to confirm the information it receives, our internal accelerometers can lead us astray. For example, if an airplane is stabilized in a descending spiral and there’s no change in pitch, roll, yaw, or velocity, once fluid in our semicircular canals gets used to these forces our accelerometer will tell the brain that we’re flying straight and level.

This is not a good thing. And to make pilots aware of the insidious nature of spatial disorientation, those are exactly the sensations the FAA’s Vertigon simulates.

"I Flew the Gyro"

I was seated in a darkened "airplane" resembling a 1940s-style Link Trainer. Inside, standard instruments, a yoke, and computer screen give life to the sham Cessna 172. After some brief instruction, the operator begins the simulation that includes a constant, but slow-moving gyroscopic motion that swirls the fluid in the ear’s "yaw" canal.

The spinning is imperceptible-below the fixed acceleration threshold, wherein the semicircular canals cannot sense any rotation at all. This threshold is approximately 2 degrees per second, gradual enough that the pilot won’t sense any change but will develop "the leans," a feeling of leaning or turning that can occur in the same or opposite direction of the motion.

After 10 to 20 seconds of constant angular acceleration the leaning sensation read by the brain is bogus. So far so good, though, because the horizon out the simulator’s "window" is honest.

Then the overhead speaker crackles to life: "Cessna Zero Three Two Six Tango, climb and maintain six thousand." A solid overcast loomed, but I followed instructions and entered the ashen smudge.

"Cessna Zero Three Two Six Tango, ident." Because the transponder is intentionally located deep in the cockpit, the unwary student must move his or her head on the "pitch" axis and swirl the fluid in the corresponding semicircular canal to push the ident button.

Whoa! After the instructor’s briefing I thought I knew what to expect, so I moved my head slowly and deliberately as I reached for the transponder’s ident button. But I still felt the overwhelming feeling of a sharp turn to the right. Checking my instruments revealed the counterfeit sensations.

As the simulation continued I found that I could control my disorientation by holding perfectly still (not always possible in turbulent conditions or with a heavy cockpit workload), or I could heighten the effect by jerking my head around or, more realistically, by reaching toward the rudder pedals for a dropped pencil.

In addition to the graveyard spiral sensation, the Vertigon introduced me to the Coriolis effect. Once my inner ear adjusted to the constant spinning, the Vertigon stopped turning. Because my vestibular system was still telling my brain that it was moving, I felt as if I was still turning.

This is why walking is a challenge when you get off a spinning amusement park ride and when you have good visual cues to counteract what your vestibular system is telling you! Imagine how you’d feel flying in IMC when you roll out of a standard-rate turn. The Coriolis illusion tells you you’re still turning even though you’re flying straight and level.

The door of the simulator swung open and sunlight bathed its interior. I had "survived" and was rewarded with a healthy respect for the effects of spatial disorientation and a nifty sticker that proclaimed "I Flew the Gyro."

Lessons Learned

"Your brain tells you one thing while you’re doing another," said Gene Mongelluzzo of Rockville, Maryland, who rode the Vertigon at EAA AirVenture. "It’s very impressive how real the sensation is. It’s incredible-a very worthwhile simulation." Gene has already begun his quest for his instrument rating and has had some experience in the soup with his CFII. "You better believe your instruments," he warned.

But an instrument rating-and staying instrument current-does not prevent spatial disorientation. It trains pilots to deal with-and disregard-the false sensations when they arise. "In all cases of spatial disorientation, the pilot must rely on the flight instruments when making control inputs," said Rogers Shaw of the FAA Airman Education Program in Oklahoma City. "And be patient until the false sensations dissipate."

More than just a ride, the FAA presents important information about spatial disorientation and human factors during the Vertigon briefing at EAA AirVenture:

• Rely on your vision. If outside references are available use them. If not . . .
• Rely on and trust your instruments. Stay current in the aircraft you intend to fly. Practice flying under the hood with a qualified instructor. Scan your instruments, interpret what they’re telling you, and make composed control inputs if necessary.
• Keep you head as still as possible.
• Be organized in the cockpit, especially IFR pilots about to head into weather.
• Self-imposed stresses can also contribute to spatial disorientation, including dehydration, lack of oxygen, sickness, alcohol, drugs, or prescription and over-the-counter medications.

What the Vertigon flight and briefing stresses most is that avoidance is the best prevention of spatial disorientation. If you’re a VFR pilot, do not push the weather. Land well before you blunder into a cloud and attempt the 180-degree turn that will take you out of the clouds-and set you up for a good case of spatial d.