What Is Airplane Mode, and What Happens If You Don’t Use It During Flights?

Is airplane mode a necessary inconvenience or an aeronautic myth? We unravel the science behind it and why you (still) need to use it on your cell phone.

If you’ve flown on a commercial flight more than a handful of times, you know the drill. Once the aircraft door makes that familiar “thunk” noise upon closing and that cold air starts blasting from overhead, the flight attendant will instruct passengers to switch their phones to “airplane mode.” And while it’s difficult to disconnect, especially for a flight that lasts more than a couple of hours (thank goodness for in-flight Wi-Fi!), airplane mode is a necessary inconvenience. So, what is airplane mode, exactly, and why do airlines require it? Read on for this interesting bit of airplane trivia.

What is airplane mode?

Airplane mode (sometimes called “flight mode”) is a setting on your smartphone that temporarily suspends signals and Wi-Fi, even as the rest of the device remains fully functional.

  • On Android phones, airplane mode is activated by swiping down from the top of the screen two times to open the Settings panel. There, you’ll see an airplane icon. When you activate it, your phone is on airplane mode.
  • On an iPhone, the icon for airplane mode is in the Control Center. You can access that by swiping either down from the top right or up from the bottom, depending on the age and model of your phone.

What happens when you put your phone in airplane mode? Your phone stops receiving the radio signals that enable you to send or receive text messages or calls, access web pages or web-based email such as Gmail, or download data. However, text messages that are already downloaded, as well as other stored information, may be accessible; that includes any documents, games, music, or films you’ve already saved to your device.

Why is airplane mode required?

Just like aerodynamics and the science of aviation, the reasons behind requiring airplane mode aren’t simple. But, in short, “airplane mode is required to mitigate any possible interference to sensitive airplane systems,” explains Ryan C., a commercial airline pilot who asked to remain anonymous. These are communication and navigation systems that utilize radio frequencies emitted from the ground. They’re the most vulnerable to radio-signal interference, he explains, because those same frequencies are used by cell phones and tablets. “The radios for Wi-Fi, Bluetooth, voice calling, 3G, 4G, and 5G data all use different parts of the radio frequency spectrum.”

The problem occurs when crosstalk or adjacent-channel interference (ACI) becomes an issue. “ACI essentially means that one radio receiver can inadvertently pick up a transmission from a transmitter on a nearby frequency,” Ryan says. That transmission can interfere with the intended signal. He uses the analogy of listening to analog FM radio in your car and not being able to hear a song clearly because you picked up a transmission from another station that’s transmitting on a nearby frequency. On an airplane, if your pilots are navigating a tricky landing or there’s a very real emergency onboard or on the ground, their communication lines with ground control need to be clear and wide open, and an errant cell phone call can compromise that.

Ryan says that airplane mode has become “distinctly more critical” with the rollout of 5G by several cellular service providers. Even though airplanes fly up to 40,000 feet in the sky, “for the first time,” he explains, “the signals generated from ground antennas and people’s 5G devices might cause interference at the most critical time of flight,” since they’re very close to the signals used by the airplane’s radio altimeters, which bounce a radio signal off the ground and then back to the airplane’s antenna.

So during descent and landing, especially, that interfering signal could make it difficult for the cockpit to discern how far the plane is from the ground—not a situation anyone wants to be in.

What about in-flight Wi-Fi?

Most airlines now offer in-flight Wi-Fi as a paid service. So why doesn’t that interfere with aircraft communications? Since Wi-Fi functions with satellite signals rather than radio signals, it’s not connecting to cell phone towers on the ground. That means if you’re willing to pay for it—and potentially put up with slow or spotty connection speeds—you can stream video, surf the Internet, and download data while you fly.

Still, on domestic U.S. flights, at least, you can’t make calls using VoiP programs like Skype, WhatsApp, or FaceTime. We suspect that has a lot to do with industry concerns about distracted and disruptive passengers, especially those who opt to conduct all their calls on speakerphone.

What happens if you don’t put your phone in airplane mode?

If you forget to put your phone in airplane mode or purposely try to flaunt the rules, the chances of a disaster are remote. But the consequences of an error could be deadly, so you don’t want to chance it. Commercial pilot Ryan explains that pilots use the plant’s radio altimeters to know the exact height of the airplane above the terrain below. They especially rely on this data during approaches to land when there is very low visibility due to fog, snow, or other bad weather.

“Airplanes that are capable of performing an ‘auto-land’ procedure, where the airplane’s autopilots land the plane without control inputs from the pilots, must have reliable information from the radio altimeters, or these landings in low visibility would not be possible,” says Ryan. “The fear is that if a passenger’s 5G capable device is not in airplane mode, it could cause a spurious signal to be picked up by the airplane’s radio altimeter antenna. This could possibly cause an erroneous indication of the airplane’s height above the runway. As you can imagine, this could have frightening consequences.” And it doesn’t matter if it’s one person or several who are ignoring the rules—all it takes is one errant signal and the wrong combination of circumstances for disaster to strike.

Does airplane mode save battery?

If the safety consequences of not switching to airplane mode don’t scare you, consider this: Receiving and sending wireless signals is one of the biggest drains on your cell phone battery. So switching to airplane mode saves on battery consumption simply because you can’t do as much with your phone as you would with normal connectivity. Battery savings will vary from device to device, but using airplane mode during your flight means that when you do land, you’ll have a better chance of having enough battery to call your loved ones or a taxi, check email, or find directions to your hotel.

Elizabeth Heath
Elizabeth Heath is a travel and lifestyle writer based in Italy. Her writing on travel and sustainability appears in national and international publications and she is the author of several guidebooks. For RD.com and sister publication FamilyHandyman.com, she writes about pets (especially dogs!), books, seasonal gift guides, home improvement, and outdoor living.