What happens when you don’t put your phone on airplane mode on an airplane?

published: Sep, 20, 2023

by: guestposts

Your phone will probably annoy a few pilots and air traffic controllers.  But, most likely, not badly enough for them to take action against you, if that’s what you want to know.

You may have heard that unpleasant noise from an audio system, that occasionally happens when a mobile phone is nearby (see also Coenraad Loubser’s answer).  A phone’s radio emissions can be very strong, up to 8W; they cause this noise due to parasitic demodulation.

actually heard such noise on the radio while flying.  It is not safety critical, but is annoying for sure.

Of course, there is plenty of attenuation between phones in the cabin and the pilots’ radio.  However, if say 50 people on board are inconsiderate enough who can’t be bothered to switch their cell radio off, there will be 50 phones constantly looking for cell towers at maximum power.  That is a lot of radio pollution.

When inflight cellular service is provided, there is a cell station right beside those phones.  They communicate at very low power without causing any disturbance.

Wi-Fi signal is much weaker (100mW) than GSM at its peak, and I never heard of it causing any problems.

It is common courtesy.  By switching your phone to airplane mode you show your appreciation to the people doing their job to get you where you want to be.

I am not an electrical engineer, but I am an airline pilot.

I’m going to blow the mind of every frequent flyer out there and say this: cell phones can and do interfere with airplanes. Transmitting cell phones can cause audible interference on the aircraft’s radios. You’ve probably heard this interference yourself when a phone is set near a speaker. It sounds like a “dit-dit-dit-dit” tone and it’s pretty annoying. Anyone who has had to track down audio interference in a sound system understands.

So, if cell phones actually DO interfere why haven’t I heard about it?
First of all, it’s fairly rare. The interference doesn’t happen every time a phone is on inside an airplane. I hear it maybe once or twice a month, and I fly about 50 flights every month. So it’s rare, but I’m guessing 2-3% of the flights is a lot more common than the “once in a million” or “never” that most people guess. It’s usually spurious. It happens once or twice and that’s it. Here are a few of the factors that determine whether or not a phone is going to blast the pilot’s ear:
1. Timing. Most of the time, the phone has to be actively transmitting at high power to cause the audible interference. That means it needs to be sending or receiving a call at the edge of cell reception, which is usually around 5,000 to 10,000 feet. On the ground with good reception it’s rare to hear the interference (but not impossible) and for most of the flight above 10,000′ you don’t have reception and your phone is just blissfully draining its battery in peace.
2. The phone. Some models are worse than others, with GSM phones being some of the worst offenders. And as time goes on, I’m hearing it less and less as phone technology advances.
3. The airplane. My personal opinion is that size is more of a factor than age here. Most of my flight experience over the past decade has been in smaller regional jets. An electrical engineer will be able to give you equations about field strength and dropoff over distance. I’m not an electrical engineer, so I’ll sum it up and say that you have to be pretty close to the radio equipment for your phone to interfere. So in a 767 with a wide fuselage and a galley between the cockpit and first class there might not be any passenger seat close enough to radio equipment for a cell phone to interfere. On a RJ, the first few seats can be within ten feet of the pilots’ radios.
All of these have to coincide for a phone to cause audible interference.

Secondly, and in the interest of full disclosure…it’s usually a crewmember’s phone. As I said, distance is a key factor and the pilots and forward flight attendants sit closest to the radios. When we hear the “dit-dit-dit-dit” over the radio the conversation usually goes like this:
Pilot 1 <sing-song voice>: Some-body left their phone on.
Pilot 2: Not it.
Pilot 1: Probably the flight attendant’s.
(There’s a 30% chance it WAS Pilot 2.)

In any case, it’s not worth making an announcement to the passengers when it’s probably only going to happen once. It’s definitely not worth doing extra paperwork by reporting it to the FAA.

But wait! If airplanes can be affected by my cell phone why allow them on the plane at all?
If you ask me if phones interfere, I’ll say yes. If you ask if they’re dangerous…eh, not really. It’s annoying, but the practical result of this interference is that the radio frequency is blocked for a few seconds. Pilots train regularly to deal with an engine failing right as they’re taking off. They train for fires, for flight control failures, for losing their instrument readouts, for having their instruments suddenly go wonky, for recovering from wake turbulence that rolls the aircraft wings-vertical, for losing the hydraulics, for losing all electrical power. They know procedures for losing all onboard navigation. There are procedures for losing all onboard radios that they learn early on in flight training. If you ask an airline pilot to name one thing that could cause an airliner to crash out of the clear blue sky besides a bomb or missile, they’re going to be thinking for a while before they say “Oh, yeah! Geese.” They’re definitely not going to say, “Well, having a radio frequency blocked for two seconds would do it.” The same practical effect happens when two people speak at once on the frequency and that is happening somewhere in the world at this very moment. Since the actual danger posed to the aircraft by an interfering cell phone is much lower than…well, any one of a hundred things that regularly exist on an average flight there’s no point in banning phones from airplanes.

Would I get in trouble if I accidentally leave my phone on and it interferes?
Probably not, for all the reasons I mentioned above. It’s just not worth it generally for the crew to hunt down a phone that generates a bit of noise on the radio. And pilots are allergic to paperwork, so it really wouldn’t be worth it to report a passenger to the FAA. That’s technically possible, but practically speaking it’s not going to happen unless the passenger refuses to stop texting when they’re asked to put their airplane mode on.

What’s the worst that could happen from this interference?
There are older reports about phones causing navigation needles to jump around, but I’ve never seen that effect myself and I’m guessing that those were all back in the past when electronic shielding was not as good as today.

The most serious case I experienced was a few years ago when a passenger at the front of my small regional jet was holding a long text conversation on his GSM phone as we were being vectored for approach below 10,000′ on a very busy radio frequency. It was the perfect storm of cell phone interference. Every time he sent a text we’d get the “dit-dit-dit-dit” on the radio. From our end, it just meant that the typically spurious interference was not spurious this time and it was making us miss radio calls. The second time we missed a radio call ATC started using their exasperated “talking to a small child” voice.
“JetWeasel 1234, Des-cend to FOUR thou-sand. And listen up.”
We called the flight attendant, who assured us her phone was off and then noticed 2A was surreptitiously texting on his phone and trying to hide it. She told him it was interfering with the cockpit and he quickly turned it off. The interference stopped. Did he get in trouble? No, what would be the point? Like every other passenger he thought that the “interference” thing was a myth. He turned it off when asked, so no big deal.

But…a few weeks ago at Chicago Midway two aircraft with very similar-sounding callsigns were lined up on crossing runways waiting to take off. And when one was cleared to go, they both thought the call was for them and started to take off at the same time right at each other. Fortunately, Midway Tower ATC noticed right away and yelled for them to abort the takeoff. That would have been a very bad two seconds for a pilot’s radio to be blocked.

In conclusion: it’s not really dangerous to forget to put your phone into airplane mode and you’re not going to get fined by the FAA as long as you don’t argue about it. But it can be quite annoying to the pilots and it’s going to drain your batteries. So please turn your airplane mode on, sit back, relax, and enjoy your flight.

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