What scientists haven't solved and hot-shot pilots won't talk about.
- By William Gregory
- Air & Space magazine, May 2002
One of life's humbling moments comes for the fighter pilot racking the simulator around at 30,000 feet with the bad guys closing in. Even though he has a thousand dogfighting flight hours and is attached to the ground like a slab of granite, he feels airsick. Why does it hit him in the simulator but not in his airplane?
Every time he takes to the sky, the pilot takes in hundreds of physical cues, some very subtle, that help orient him within the cockpit. Even the best simulators can’t reproduce something as seemingly inconsequential as the odor of hydraulic fluid. For a veteran military pilot, such omissions might cause disorientation, which in turn can bring on waves of nausea, sweats, irregular breathing, vision disturbances, and other symptoms of motion sickness.
Ron Kruk, a motion sickness expert for CAE, a Canadian company that manufactures simulators, says, “A simulator can’t replicate the real world completely, like giving the acceleration of a real aircraft. Parts of one’s nervous system are fooled by that and other parts are not. So you get sensory mismatches. Simulator sickness is a special case of motion sickness. Maneuvers that get you sick in a simulator might not get you sick in the aircraft.”
Scientists don’t fully understand why a pilot can feel fine in a simulator one day but turn green the next, but they do know that disorientation often originates in the inner ear, where tiny hairs, or otoliths, can indicate you’re stationary when your eyes say you’re not. So even though the pilot feels his feet on the floor and his inner ear says everything is straight and level, the simulator’s electronic scene tells his eyeballs that he’s in a steep bank or, worse, a roll.
To get reoriented, a pilot might have to step back for a moment and sit quietly. But, as Captain Angus Rupert, a flight surgeon at the Naval Aviation Aeromedical Research Laboratory in Pensacola, Florida, points out, “These are people who do not tend to say ‘Hey, I have a minor problem here.’ They don’t even say anything when they have a major problem.”
The military itself is unwilling to say it has a “problem” with motion sickness. The official response from Colonel James Little, who directs the motion sickness training program for the Air Force: They weed out the most sensitive recruits early on so it rarely becomes an issue. But the military and NASA currently fund the bulk of motion sickness studies, including investigations into simulator sickness, so they’re obviously looking for answers.
People like Kruk contend that airline and military transport simulators have reached a stage of fidelity that eases adaptation. But even the less susceptible pilots can face discomforting electronic aberrations, like jitter, which is analogous to the flickering of a TV screen. More disconcerting is latency, in which too many milliseconds pass between the time the pilot moves the stick or ailerons and the time the scene responds. Another problem is off-axis viewing, in which the student flying is fine and the instructor to the side is uncomfortable. High fidelity or not, simulator software and hardware have to be in tune.
Dennis McBride, a physician and former executive director of the Institute of Simulation and Training in Orlando, Florida, believes that superhigh fidelity in the newest simulators actually causes the trouble. The higher the fidelity, the more likely experienced pilots in particular will run into problems. No simulator can offer a perfect reproduction of all the forces at work in a modern jet in flight.
McBride recalls one dilemma the Navy faced with the A-12 stealth attack airplane before the program was canceled. Its concept of operations, he says, called for intense shipboard simulator rehearsal just before a mission. Since adaptation to minute changes in cues is a factor in motion sickness, McBride says, a pilot could adjust to the simulator and then get disoriented in the real airplane, where his performance could deteriorate.
Exactly how much the disconnect between a simulator run and a real flight can affect performance is unclear. Several researchers believe not enough work is being done on this crucial issue. While no one could cite an instance of a pilot crashing a jet or even getting in a car accident after an extended stay in the simulator seat, there’s plenty of evidence to suggest such a mishap is possible.
William Ercoline is a former instructor pilot who has taught in heavy, motion-based simulators and now works on spatial disorientation countermeasures at Brooks Air Force Base in Texas. He says that once a pilot becomes stressed, “he is more likely to experience what we call Type One disorientation, which is unrecognized. That means he or she will start focusing on one thing and let another go, and it could be the attitude of the airplane. I’ve seen that. I have some friends that do aerobatics and they get this thing called the wobblies, which causes long-term effects. They start driving their cars, start shaking, and have to stop.”
Kay Stanney, an industrial engineer at the University of Central Florida, tells of a helicopter pilot who, driving home after a long hop in the simulator, suddenly “saw” his car roll upside down. Though he got the car off the road and his head right side up, the experience has become a legend in the small world of simulator sickness research. Robert S. Kennedy, a Navy flight surgeon and expert on motion sickness, tells a similar story about an operator of a Navy Landing Craft Air-Cushion vehicle (LCAC): After getting out of a simulator, he began weaving so much on his drive home that cops pulled him over for drunk driving. The man was having a post-simulator disorientation flashback.
Disorientation can happen in flight because of the same man-versus-machine disconnect. A high-time Navy pilot, who asked not to be identified, remembers a night bombing drill in an A-7 in which he could see the lights of the target ship through the windscreen, paired with its FLIR (forward-looking infrared) head-up display image. Abruptly the FLIR ran out of gimbal travel and the two scenes diverged. “I had an overpowering wave of nausea,” he recalls, “but I had enough instinct to pull back hard on the stick.”
The Federal Aviation Administration and the military have established limits on the amount of jitter and latency that can take place in a simulator, but no standards exist for helmets. In one study Stanney and Kennedy found that about 10 percent of simulator users reported vision-related symptoms, like a headache, another 7.5 percent reported nausea, and five percent suffered from disorientation. While using a virtual reality helmet, a remarkable 25 percent experienced nausea, and another 30 percent reported disorientation.
A full-motion simulator can cost $10 million to $15 million, while a helmet costs maybe $50,000, which helps explain why the military still uses them, even though they are more likely to cause motion sickness. Indeed, military instructors are incorporating more helmet displays into flight simulators; well engineered, these can work just fine, says Kruk.
Helmet displays are important for reconfigurable helicopter simulators, like the one in an Army program that can be changed from a UH-64 Apache to a UH-60 Black Hawk by switching moveable cockpit modules around and exchanging virtual reality software. Engineers still have to make sure the tracker beacon in the headset stays in sync with the scene that rolls by on the screen.
Researchers like Kennedy are looking into the causes of all of these reactions and hoping to find a way to counteract some of the more dangerous side effects. In his office, Kennedy has a seven-foot-wide, six-feet-high drum made from aluminum stringers, which he uses to conduct tests on motion and peripheral vision. He’s wrapped a corrugated-cardboard skin around it and pasted some cheap wallpaper with a nauseating horizontal ocean wave pattern on the inside. The test subject sits in a chair two feet off the floor with nothing much visible except the wallpaper.
“Close your eyes,” a Kennedy aide says to a young man in a demonstration run, whereupon the drum gradually spins. When the speed tops 130 degrees a second, the aide gives an “eyes open” command. All the subject sees is a fast-moving ocean scene turning right. But as the drum accelerates toward its maximum, 160 degrees a second, the ocean scene seems to stop and the chair appears to spin left.
No question, it’s quick and queasy, a classic case of the inner ear saying “You’re not moving” and the eyeball saying “Oh yes you are.”
David Graeber is writing a doctoral dissertation on the reactions of volunteers spinning in Kennedy’s drum. His findings reiterate what pilots and sailors learn on the job: Adaptation is the key. When you’re in a simulator, don’t try to bull your way through motion sickness, something hot-rock pilots, disdainful of electronic flying, are prone to do. Back off, get acclimated in short bursts.
Neal Finkelstein, an Army computer engineer, is dealing with the “tough guy” problem among infantry who use virtual reality helmets for battlefield simulations. Even though they have their feet planted firmly on the ground both in the chair and on the screen, “one in five is the drop-out rate,” he says, “and we’re still trying to figure out why so many people are getting sick. These big Army guys get in there and say ‘I’m really tough.’ But the more they fight it… They’ve got to back away.
“Helmets are tougher than screens. No other reference point is visible in a helmet, just that claustrophobic type of environment. Moving the head is not something people think about; they just automatically move it.”
Kelly Kingdon, a Canadian studying cyber-motion under Kay Stanney, shows off the test rig, one that comes closer to Kennedy’s wallpaper drum than what pilots meet in a simulator. A computer program generates a maze of three long corridors and 29 rooms onto a display in a Virtual Research B6 helmet, which has micro-optics that produce realistic immersion in a scene flowing by, comparable in quality to graphics on a home computer.
A single trip through the maze, self-driven with a standard computer mouse, takes 15 minutes and includes a set of mouse-actuated tasks. As you move through the corridors, various “jobs” pop up: Find the door to the hall in a room with psychedelic-colored walls; put three shapes—a star, a cylinder, and a circle—into slots. Throughout the test you have to keep “moving” down the hallways as synthetic scenery slowly flows by. If you move too slowly the scene goes into a roll. Though not as overpowering as being in Kennedy’s drum, the experience can be unsettling if the test goes on long enough.
Stanney’s students have put over 1,000 student volunteers through the test. Unlike pilots who go through screening, 90 to 95 percent of the students reported at least one symptom, like a headache, but only 1.5 percent got violently sick. Rupert says that in rare cases such symptoms can last for a month or two.
All of these tests have provided some basic answers, with more subtle solutions perhaps to come. Improving the technology for the virtual reality helmets will help. So will getting tough guys to back off and, just as important, hard-driving instructors to lay off.
When an instructor flash-freezes the simulator at 500 knots (575 mph) to start a new dogfight and cram in more combat per hop, he makes the student feel as though he’s smacked into a mountain. When a pilot’s cold grounds him, the first thing the operations officer does is send him to catch up on his simulator syllabus. Feeling below par, maybe with ear complications, the pilot is all set up for simulator sickness. None of these problems might be life-threatening, but what if the same pilot winds up in a regular cockpit the next day still feeling sub-par and slightly disoriented, because of subtle discrepancies between the simulator and his cockpit?
Researchers like Kennedy are trying to come up with basic guidelines to prevent such problems, including making sure pilots take shorter runs in the simulators. Both the Air Force and the Navy have tried adaptation drills. The Naval Aviation Aeromedical Research Laboratory in Pensacola, Florida, has a 20-foot rotating room called the Coriolis Acceleration Platform, in which people have lived as long as six weeks. The room constantly changes the rules of orientation. “It rotates very slowly,” Rupert says, “three revolutions per minute, one every 20 seconds.
“It’s like flying a single-engine piston aircraft,” he continues. “When you push the nose over, it tends to yaw to the left, because that blade in front of you is rotating clockwise. The same thing happens in the inner ear, in those little canals, in the rotating room.”
Because of its career-limiting implications, active-duty pilots hate talking about simulator sickness, but the longer they try to tough it out in a simulator run gone bad, the more severe their symptoms will get. Maybe they can console themselves with the knowledge that when it comes to enduring the virtual reality chair or helmet, sometimes it’s the most adept pilots who have the hardest time.
Astronauts Turn Green Too
The congressmen wanted to know if John Glenn had gotten nauseous while journeying in space. His Russian counterpart, Gherman Titov, had gotten very sick on his 1961 Vostok 2 flight, but Glenn insisted, “Oh no, of course not.” Later the American let slip, “It’s not so bad once you get used to it.” Well, if there’s no problem, what is there to get used to, asks flight surgeon and motion sickness researcher Captain Angus Rupert, after telling the tale.
After decades of putting up a macho front, U.S. astronauts are finally fessing up to their struggles with motion sickness. In a recent report on space physiology, Deborah Harm of the Johnson Space Center in Houston, Texas, found that U.S. astronauts reported no symptoms with Mercury and Gemini, but the number of crew members reporting symptoms rose to 35 percent for the Apollo program and 60 percent for Skylab. Currently, Harm and her co-workers write, ”it is estimated that 80 to 90 percent of all shuttle crew members experience some symptoms of motion sickness.”
Harm says astronauts still don’t talk much about ”flashbacks” and spaceflight illusions. Sometimes in space they wake up and can’t sense where their legs and arms are. One Russian cosmonaut went to sleep on the Mir space station with his arms folded and when he woke, he was certain that they were still crossed; in fact, they were raised straight up.
Sometimes illusions persist after landing. One astronaut reported that on his first night back on Earth, he had the sensation of rolling over in bed, so he grabbed the edge of the bed to keep from ”falling” onto the floor. All the time he was lying flat on his back. Some astronauts report that while climbing stairs, they feel the stairs are coming toward their feet, rather than vice versa.
”Astronauts are missing the key most important piece of information: where is down,” says Rupert. ”On the ground,” he adds, ”left and right, up and down have meaning. But not in space. People get disoriented very quickly.”
When astronauts lose their reference point in space, they instinctively choose to align with either the visual scene around them or their bodies’ vertical axis. The former group have symptoms that are more severe and last much longer in spaceflight than the latter, says Harm.
The Johnson center has two simulators that help prep astronauts for situations in which the inner ear may feel a tilt but the eyes see everything as linear. And when the eye and ear don’t agree, motion sickness can kick in, even among the most experienced astronauts.