Why are airplanes so cold? It’s for your health.

Popular Science...

I was recently preparing for a long-distance flight, when a friend took note of what I was packing in my carry-on. Along with my daily essentials, I’d stuffed in a puffy jacket, thick socks, and a winter hat. “Aren’t you heading to Vietnam?” He asked. “I’m pretty sure it’s hot there.”

“These aren’t for Vietnam,” I told him. “They’re for the plane.” 

Airplane cabins are kept notoriously cold. What’s more is that these frigid temperatures are absolutely intentional, Bobby Laurie, a former flight attendant and co-host of the travel and lifestyle talk show, The Jet Set, tells Popular Science.

“Look at the flight attendants next time you’re boarding a plane,” says Laurie. “It might be July in Miami and a temperature of 95 degrees outside, but they’re all wearing jackets and sweaters. They don’t really care what’s happening on the other side of that airplane. They’re prepared for what’s going to happen inside.” 

Popular Science turned to Laurie to fill us in on the scientific reasoning behind this excessive chill, and to find out why flight crews don’t just turn up the temp on planes? In the end, all that cold air is about much more than personal preference. 

An airplane’s average temperature and the reasons behind it

“The sweet spot for a plane’s cabin temperature is somewhere between 70 and 75 degrees,” says Laurie. It’s an indoor temperature that in most cases feels comfortable. But since airplane cabins are already kept at a lower humidity (typically ranging from 10 to 20 percent at cruising altitude, drier than most deserts) to help prevent frame corrosion, the air can feel much colder. 

Most commercial airlines keep their cabins in this temperature range for one main reason: to prevent passengers from fainting. On a plane, the danger of someone suffering hypoxia, a condition in which a person doesn’t get enough oxygen, often causing them to pass out, is a real possibility. 

In fact, passengers fainting on planes happens more often than you might think, says Laurie. It’s especially common on red-eye flights. “People tend to be a little disoriented when they wake in the middle of a flight,” he says. “Many times, they’ll just stand up and immediately hit the floor.”

This is due to the cabin’s simulated air pressure, which typically remains at an altitude equivalent of between 6,000 and 8,000 feet above sea level. It’s a mountain-level elevation that acts as a compromise between maintaining the plane’s structural integrity (sea-level altitude at a cruising altitude of 35,000 feet would force the plane to be excessively heavy and fuel-inefficient) and keeping passengers comfortable. 

While most people on board don’t even notice this air pressure adjustment, your body has access to about 25 percent less oxygen than at sea level. Those who aren’t used to it can get dizzy or lightheaded. They might even faint. 

To combat this risk, flight crews turn down the heat. Not only does cold air keep passengers more alert, essential for responding to sudden turbulence or an efficient evacuation, but warm temperatures make it harder for your body to maintain circulation and cause your heart to pump faster, which requires more oxygen. 

Cold air, on the other hand, helps to slow your heart rate, keeps your breathing steady, and helps to stabilize your blood oxygen levels. It also wards off nausea and motion-sickness by calming your body’s temperature-control system and bringing it into balance. 

Keeping the airplane cabin colder also helps regulate humidity inside, says Laurie. Typically, the cabin’s already low humidity levels would cause any moisture on your body to evaporate more quickly and cause immediate dehydration. But pumping up the air prevents passengers from getting too warm, which slows that evaporation from happening. It also counteracts the moisture vapor in the environment, making your surroundings feel less stuffy. 

How body heat affects temperatures 

Chances are you often find yourself piling on layers at the beginning of a long-haul flight, only to be peeling some of them off somewhere over the Pacific. That’s because having hundreds of passengers packed so closely together in an enclosed cabin can really drive up temperatures. 

Think about it, says Laurie. You’re likely covered in a blanket. Maybe you’re donning a hoodie to keep your head warm, and the person next to you is literally inches away. “With everyone’s collective body heat,” he says, “you’ll probably start to get really warm.” 

Keeping the cabin cooler helps to mitigate this natural heat influx and keep everyone more comfortable in the long run.

Who controls the cabin temperature?

It depends on the airplane type. “Both Airbus and Boeing operate completely differently,” says Laurie. On Boeing airplanes, the temperature in the cabin is controlled from the flight deck, a.k.a the cockpit. “So [pilots] are adjusting the temperature to what they think it needs to be, but they’re not actually back there.” 

Airbus planes allow flight attendants to adjust actual cabin temperatures via a central touchscreen, while Boeing generally relies on rudimentary rotary knobs calibrated with general “cool” to “warm” ranges instead of exact numerical values. 

Still, all commercial planes have an integrated Environmental Control System (ECS) that manages the aircraft’s cabin pressure, temperature, and air quality. An ECS distributes conditioned air to several distinct zones throughout the aircraft. 

The flight deck has its own dedicated ECS zone, since this area of the plane is filled with heat-generating navigation, communication, and radar equipment that require dedicated cooling. 

However, the passenger cabin is usually separated into two to four independently controlled temperature zones (for example: forward, mid, and aft). This allows flight attendants to turn down the air in, say, the plane’s mid-cabin, which tends to generate the most body heat, while keeping the back of the plane cool. 

To manage the temperature in each specific zone, aircraft utilize trim air valves. These specialized components introduce small amounts of hot or cold air into the main airflow ducts, allowing for customized temperatures specifically tailored for each localized zone. 

“If you’re walking to the back of the plane, you might even feel a change in the air a time or two,” says Laurie. 

Where to sit if you run cold 

Along with carrying a hoodie, there are other ways to escape the cabin chill. Avoid sitting in an exit row, since frigid air can seep in through the door seals. Window seats also tend to be cooler, as they’re closer to the outside of the plane. 

“The galleys,” those designated kitchen and prep areas on an aircraft, “are always colder than the rest of the plane,” says Laurie. Not only are they usually located right near an airplane door, but they’re also home to the powerful galley cooling units planes use for food storage. 

Ultimately, everyone’s body temperature is different, and how you perceive heat varies. “Say you’re on a domestic flight along with 150 to 200 other passengers,” says Laurie. “It’s going to be hard to make everyone happy at the same time.” Instead, he suggests, pack that carry-on bag accordingly!

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