Hot seat – ergonomics of airline seats
Mary Roach
Midway through a five-hour flight to New York, the man in 23C unfolds his knees from his armpits and leans over to see what I’m reading. It’s a research paper entitled “The Assessment of Chair Comfort.” The paper is open to an 11-point Comfort-Discomfort Scale used by subjects to describe their feelings at the end of three and half hours spent sitting in a chair. My neighbor takes a pencil from his pocket and checks numbers 7, 8, 10, and 11: I feel cramped. I feel stiff. I feel sore and tender. I feel unbearable pain.
To make him feel better, I tell him that directly following this flight, I’m taking a train to Melville, Long Island, where I will spend another two hours sitting in an airplane seat, this time going nowhere, without even so much as a bag of peanuts for my troubles. I’m to be a test subject in an ergonomic assessment of United Airlines’ new economy-class seat cushions. Working with an ergonomics con sultancy called BCAM International, United has already designed and tested fancy new ergonomically correct first-class “bed products” and new mega-adjustable “Connoisseur” class seats with motorized muscle-relaxing lumbar support.
Ergonomics is the science of equipment design: a marriage of biomechanics and engineering whose aim is to prevent injury and discomfort. What started with factory assembly lines and office chairs will in the next few years spread to just about every facet of every human environment. If ergonomists have their way, future products won’t be built for some hypothetical average person but will conform to the biomechanical needs of whatever particular human body happens to come into contact with them. Several projects at BCAM (the letters used to stand for Biomechanics Corporation of America, but now, after some corporate undating, stand for nothing) will bring that vision a step closer to reality. With BCAM’s help, for instance, Black and Decker drills will soon be better balanced and safer to use. Ditto Stanley hammers. Newly patented jackhammers will be outfitted with Lift-Assist, a pneumatic blast of air that propels them out of the pavement after each hammering. Later this week BCAM will be taping electrodes to subjects wielding garden pruners, to measure their muscle use.
Heading the United project is mechanical engineer Tom Cassar. Airplanes are something of a specialty with Cassar. He can tell you all about seat-belt geometry and arm-cap tilt. He knows the effect of a female twoinch heel height assumption, the knee angle of the seated human body as it relates to leg rests, the dynamic relationship between backrest and seat-pan angles.
Cassar is showing me around BCAM’s Ergonomic Seat Assessment Laboratory, which looks less like a lab than someone’s eccentrically appointed living room. Assorted bucket seats uprooted from cars lean against the walls, along with a wheelchair, a mattress, two living-room recliners, and eight airline seats. best that ergonomically correct seating has to offer. He ushers me into a Cadillac seat outfitted with a BCAM invention called Intelligent Surface Technology.
“Ready?” says Cassar.
“Ready!” I’m trying to be excited, as excited as a woman can possibly be about a car seat, which isn’t all that excited. Cassar presses a button. The seat begins making a sound like a garbage compactor. The sides begin to rise up around my thighs, and the back presses in on me, as though perhaps it will soon reduce me to a space-saving two-foot cube of journalist. Somewhere short of death by car seat, the movement stops. It is now my ideal seat. Beneath the upholstery are ten air cells that inflate as needed to customfit the curve of my lumbar spine and cradle the sides of my thighs to better distribute their weight. The brain of the Intelligent Surface is a computer program called ASCTec (which I misheard as something different).
Now, I drive a 1966 Volvo. My car seats are not intelligent. They are dumb as bricks. I love this seat. This is the most comfortable car seat I’ve ever sat in. Wait, Cassar tells me, it gets better. Every four minutes, the intelligent seat readjusts itself, in case you’ve moved. There’s even a massage option. Eventually, all airlines will have first-class and business-class seats outfitted with Intelligent Surface Technology, as will dozens of other luxury automobiles and, um, sneakers. Reebok has a license to BCAM’s technology. (As the control box is the size of a car radio, the footwear version won’t be making its debut anytime soon.)
As for those of us flying economy class? Will we, too, have Intelligent Surfaces to sit on? Not likely. Domestic economy-class seats must double as flotation devices, which limits what airlines can do with them. (Business, first class, and international economy seats have actual life jackets stashed under the seats, which costs more but allows you to design a cushier chair.) Economy cushions are basically, in the words of United’s manager of aircraft interior planning Bob Ketelsen, “a chunk of Styrofoam surrounded by foam”–foam that’s been fire-hardened to resist combustion. In keeping with the FAA’s flammability rule, the entire airplane interior–upholstery, plastics, cushions–must meet stringent criteria regarding the temperature at which the materials start to burn and the amount of toxic gases released when they do. Which explains the ugly factor: only a few manufacturers make these materials, and aesthetics doesn’t figure high on their table of priorities.
Those FAA regulations are why airlines can’t simply buy up a bunch of Sharper Image massage recliners and bolt them into place. It’d be cheaper, but they wouldn’t be strong enough. Airplane seats have to hold up under the force of 16 g’s–the new FAA dynamic certification requirement for crash survival. Sixteen g’s means 16 gravities: a force equivalent to 16 times the weight that the seat would ordinarily have to hold. Making a seat that strong isn’t, in and of itself, a huge problem. It’s making it strong and lightweight that’s tough. (The heavier the seats, the more fuel the plane burns.)
Barring intelligent air cells, how do you make a seat that fits everyone? You can’t simply design for the “average” flier’s measurements, since that would exclude more than 50 percent of the population. Everyone bigger than the fiftieth percentile–the mean on the curve–would find the seat uncomfortably small.
What ergonomists do is this: First they gather anthropometric databases for every ethnic group they expect to be serving. Anthropometry is a queer little science. There are people out there who have made it their life’s calling to measure thousands of people very, very thoroughly. Thanks to their efforts, it’s possible to know, say, how likely a sitting American female is to have thighs wider than 10 inches. Or the percentage of Japanese men with a greater-than-20-inch buttock-popliteal length–that is, the distance from the popliteus (back of the knee) to the end of the “buttock plate.” (In the name of decency, ergonomists employ an impressive variety of tush-related euphemisms. “The ischial area” is a nice one, as is “sitting bone,” the point in the middle of each cheek where the pelvis hits the chair. The fold between buttock and thigh? “The gluteal furrow.”)
Anyway, to fit all populations, the ergonomist designs a seat that fits the extreme percentiles of both the smallest and largest populations. In the case of United Airlines’ new business (Connoisseur) class seats, for instance, the seats fit everyone from the fifth percentile South Chinese woman–four feet eight inches, smaller than 95 percent of her compatriots–to the ninety-fifth percentile northern European male–six feet three inches, larger than 95 percent of his kind. (Fitting everyone isn’t feasible: to accommodate the less than 1 percent of the population that lies beyond either of these extremes would require 50 percent more adjustability.)
In between this odd couple of the tiny Asian and the gronking European sits 99.7 percent of the globe’s population. How to make a chair that fits them all? A lot of adjustability (the new United business seats have adjustable headrests, bottom cushions, leg rests, and lumbar supports). Or, in the case of economy-class seats, very little contouring. The more neck and lumbar contouring a chair has, the fewer people it fits. Worse than an uncontoured seat is a contoured seat that fits someone else. The ill-fitting concavities cause “hot spots”–points of high pressure that become uncomfortable over a long-haul flight And so we have the modem airplane seat: flat as a door and almost as hard. It’s the “almost as hard” that United is working on today. A seat tbat’s too hard is the other main source of hot spots. When you sit on an unpadded surface, half your body weight is pressed onto 8 percent of the sitting surface of your body. As time passes, this weight causes the sitting bones (also known as ischial tuberosities) to sink into the buttock tissues, which means less tissue suffering more pressure. About an hour is as much as most people can take. (Yes, Virginia, studies have been done.) Add an inch of padding, and the average sitter can endure three hours. Padding increases the contact area with the seat and distributes the torso’s weight.
Too-soft padding, though, can be equally troublesome. The padding at the front of the seat and the top of the backrest, places where there’s less body weight, doesn’t compress, and the poufing-out of the ends of the cushions forces the knees up and the upper back forward. This reduces the angle between the thighs and the torso, straining the back and crowding the abdominal organs.
In their Goldilocks quest for just-right chair cushions, the ergonomists of scAM are enlisting the aid of a dozen seasoned fliers. In addition to the subjective opinions of human beings, ergonomists often rely on computerized “high-resolution humanoids,” faceless 3-D computer-generated creatures who sit, lift, carry, and reach for as long and as often as the program tells them to. The program–in this case, an ergonomic modeling software called MQPro–then calculates how likely said humanoids are to incur an injury, and what needs to be done to prevent it. In designing leg rests for United’s Connoisseur class seats, for example, the fifth percentile South Chinese female humanoid, whose legs exert 11.05 pounds of pressure on the horizontally extended leg rest, was deemed able to exert the pounds of pressure needed to stow the thing. And so, therefore, were all the others.
Cassar seizes a lull in the conversation to request that we get started on my seat assessment. My first task, for each of four seat-pan, three backrest, and four back-contour cushions, is to sit, to sit and feel. Fifteen or tweny minutes for each cushion. Cassar ushers me to the first seat pan. I sit. I think about my sitting surface and whether it’s being well served by this cushion and how it might be better served. I think about how happy I am that I didn’t sign up for the Connoisseur class assessment, which entailed sitting through an eight-hour simulated flight in a basement lab where the air conditioner “sounds just like a jet engine.”
Next we move on to the objective portion of the ergonomic assessment, which involves something called computerized pressure mapping. Cassar spreads a piece of plastic over the seat cushion, as though perhaps someone from the airline had spoken to him about my tendency to get fidgety and spill Bloody Mary mix. The plastic pad is connected by a cord to a computer console. Inside the pad are pressure sensors that feed into the computer.
When I sit down, a horseshoe-shaped, rainbow-hued mountain range appears on the computer screen. “That’s you,” says Cassar. More precisely, it is my sitting surface. The twin peaks near the bend in the horseshoe are my ischial tuberosities. If the peaks were much higher, we’d have a hot spot.
Four seat pans and 60 minutes later, at the point when more fortunate fliers are given peanuts and a beverage, I am given a questionnaire asking me to rate the relative contouring, softness, and comfort of the seat-pan cushions under study. This is harder than it sounds. What, for example, is the difference between softness and comfort? What is comfort?
“Ergonomically speaking,” says Cassar, “comfort is defined as absence of discomfort.” In that case, all these seats are comfortable. But they’re not. They’re cramped. And you can’t curl up or stretch out. Or sleep. That’s what I want from an airline seat: to be able to sleep on my eight-hour flight to London. Is that too much to ask? Cassar looks uncomfortable. He looks like a guy who’d rather be down the hall, testing pruners.
“Well, yes,” Cassar begins. “Sleep is an important activity. Our studies show you need about 48 inches between seats to be able to have a backrest angle that is conducive to sleeping. Anything less than 48 inches and your muscles can’t relax; they’re busy holding you upright.”
And the distance between economyclass seats is . . . ?
Cassar looks at his shoes. “Thirty-one inches.”
Why is United Airlines spending all this time and money figuring out the proper depth and contour of the cushions, when what people really want is room? Cassar directs a beseeching look at Jim Watson, the high-resolution humanoid coordinating United’s economy-seat development program. Watson fiddles with his cuffs. “To gain an inch of legroom,” he explains, “we’d have to take out one or two rows of seats.” This means they’d lose revenue on fully booked flights. “We’d have to raise our costs, which is not an acceptable option.” Bottom line: People choose the airline with the cheapest, most convenient flight to the place they’re going. “No one,” levels Watson, “is going to leave at noon to get two inches more legroom.”
Do roomy seats on inexpensive flights lie anywhere in the foreseeable future? According to Ketelsen, there are other ways to configure an aircraft cabin. “People submit all sorts of radical ideas. We had one group that came up with a kind of stacking concept, where the airplane floor was stepped, like theater seating, and you’d stretch your legs out over the head of the guy in front of you.” So what’s the problem? “For starters,” says Ketelsen, “you’d have to do away with the cargo hold.”
Watson doesn’t think the economy cabin is likely to change in any sigmficant way. “If we made more room inside, we’d just put more seats in.”
Watson’s buttock-popliteal length is well beyond the fiftieth percentile. “How do you like sitting in these seats?” I ask him. Watson shrugs. Airline executives, space permitting, fly first class.
COPYRIGHT 1998 Discover
COPYRIGHT 2000 Gale Group
