The last time I flew with my mum, I had my phone on while we were in the air. She had just woken up from sleep and frantically told me “put your phone off on the Plane” for fear that I had put the whole plane “in trouble”. I explained to her that my phone was on airplane mode and it was okay, so she calmed down. For my mum, the rule of putting off your phone on the plane was still a must, even years after technology had evolved and granted us the “airplane mode” fix. Just like my mum – and even me before I studied a bit of avionics –, I’m sure most people don’t know why exactly this rule exists.
I mean, what does my phone have to do with flight safety?
The simple answer is this:
Phones (and other electronic devices) could cause electromagnetic interference which could distort the radio signals used for communication and navigation.
This might still not make much sense to you, so stay with me! In this article, I will explain in detail how aircraft are able to navigate and communicate in the air. You’ll see the relevance later.
The Radio Signals Used by Aircraft
Aircraft have various instruments and equipment on board that help them communicate with the ground Air Traffic Control (ATC) and navigate from point to point in the air. These devices transmit and receive radio signals, a band of electromagnetic waves that is suitable for use in navigation and communication since they are the least energetic and consequently, the least harmful. The radio band has its own different band divisions which are allocated to different navigation and communication uses.
These divisions are:
- Very-low frequency (VLF) between 3-30 Kilohertz(kHz).
- Low frequency (LF) between 30-300 kHz
- Medium frequency (MF) between 300-3000 kHz. Note that 3000 kHz is also 3 Megahertz (MHz).
- High Frequency (HF) between 3-30 MHz
- Very-high frequency (VHF) between 30-300 MHz
- Ultra-high frequency (UHF) between 300-3000 MHz. Note that 3000 MHz is also 3 Gigahertz (GHz)
- Super-high frequency (SHF) between 3-30 GHz
Commercial aircraft mostly use HF and VHF bands of radio waves for their navigation and communication, although some navigation equipment makes use of UHF bands. Aircraft have the antennae of the various communication and navigation systems on the exterior of the plane. Their corresponding transceivers are located in the avionics bay of the aircraft. Transceivers are a coinage between transponder and receiver, meaning the devices are able to do both transmitting and receiving radio signals.
How Aircraft Communicate
Pilots communicate with the ground in 2 main modes: voice and data. Voice communication is just like a phone call between the pilot and the air traffic controller personnel on the ground. The pilot does status reports and makes inquiries about whether or not the flight path is clear to move. Data communication, on the other hand, works like a fax machine. Data messages are exchanged between the airline personnel in automated ground stations and its pilots in the air, shown on a digital screen and printed. The pilots send information such as movement reports, any abnormal status of aircraft systems, notice to airmen (NOTAM), and so on to the ground. The airline sends information about weather and oceanic clearance and so on. In case of voice communication failure, the airline can also send crucial information to ATC on behalf of the aircraft/pilot.
Frequencies between 118-137 MHz are the specific allocated VHF band for ground and air communications.
How Aircraft Navigate
You know how car drivers know where they are going because they can actually see the road, various signs, and markers of their travel status? For aircraft, the only way pilots can tell where they’re going and essentially not fly blind while they’re up in the clouds is through elaborate navigation systems. The navigation systems typically comprise beacons on the ground which interact with their corresponding onboard equipment interact with.
Some aircraft navigation systems that make use of radio signals are:
- Distance-Measuring Equipment (DME)- this operates in the UHF band with a frequency band of 978-1213 MHz. As the name implies, it is used to measure the distance of the aircraft from a fixed point. The DME transceiver sends an interrogation signal to the beacon in a ground station and then the beacon re-transmits the signal to the transceiver on board the aircraft. All radio waves move at the speed of light and since the frequency of the signal is known, the distance between the ground station and the aircraft can easily be calculated.
- Instrument Landing System (ILS)- this is used to help the aircraft navigate during approach and landing. It operates with frequency bands of 108.1- 111.975 MHz and 329.15- 335 MHz (VHF and UHF).
- Very-High-Frequency Omnidirectional Range (VOR)- this operates with frequency bands between 108- 117.95 MHz. VOR is a radio beacon that transmits signals that, when received by the aircraft receiver, can tell the ground station’s bearing to the aircraft with respect to the magnetic North. When used together with DME, VHF helps to tell the exact position of the aircraft.
- Radio altimeter- this is used during landing to inform the pilot of the radio altitude of the aircraft. it operates in the SHF band between 4.25-4.35GHz.
The various navigation equipment helps the aircraft follow the designed flight path and get to its destination. Without it, there would be no knowing where to go.
The Radio Signals Used by Phones and Why They’re a Problem
Phones also transmit and receive radio signals. Cellphone network providers have various masts with which cellphones interact.
These network providers have various networks such as:
- 2G –uses 900 MHz and 1,800 MHz frequencies
- 3G- uses 900 MHz and 2,000 MHz frequencies
- 4G- uses 800 MHz, 1800 MHz and2, 600 MHz frequencies.
- 5G- uses frequencies below 6 GHz and 24.25 GHz and above.
There is also Bluetooth used by cellphones and other devices such as headphones, laptops, and so on. Bluetooth uses the2.4 GHz, frequency band. As you can see, the frequency bands used by cellphones are all in the UHF and SHF bands.
If the phone’s network providers operate in frequency bands that are close to those used by the aircraft systems, it could cause there to be a loss or distortion of signal in the cockpit. This could look like instruments malfunctioning and giving inaccurate readings or the sound in the pilot’s headphones not being clear. When the phone is off or on airplane mode, it does not interact with its network provider’s masts, so it is 100% safe.
The general rule with aviation is to always take extra precautions than are needed. This is part of what makes aircraft the safest means of (long-distance) transport – flying has a fatal accident rate of 0.28/million flights (IATA, 2018). Thus for safety reasons, even though it is possible that phones do not cause interference with communication equipment, it is still the wiser option to keep phones off during flight phases as critical as landing and take-off. Many airlines will have you put your phones off during these periods and allow you to put your phone on flight mode for the remainder of the flight. Before this could be allowed, lots of testing was carried out to see that it was okay to just use airplane mode. All devices that could be possible sources of electromagnetic interference were tested before approval. It’s such testing that even gave the airline industry the confidence to explore having onboard Wi-Fi which is now serviced by many airlines today.
Navigation instruments’ frequency bands are typically much different from those used for communication. However, the emergence of 5G networks has caused a lot of concerns in the US as the frequency band they use is very close to that of some navigation equipment e.g. the radio altimeter. Aviators fear that the 5G towers would cause significant distortion which could be catastrophic for flight. One precaution suggested was that there be no 5G towers close to airports/airfields.
I hope this article did justice in answering your question. The next time you fly, leaving your phone on and off airplane mode might not cause the aircraft to plunge to the ground. BUT it is always better to err on the side of caution and adhere to the airline’s rules.
References
- Rfwireless-world.com. n.d. Aircraft Radio Frequencies| Aviation Radio Frequencies. [online] Available at: https://www.rfwireless-world.com/Terminology/aircraft-radio-frequencies.html
- Moskvitch, K., 2013. Why we have to turn electronic devices off on planes. [online] Bbc.com. Available at: https://www.bbc.com/future/article/20130604-why-we-turn-devices-off-on-planes
- Walton, J., 2020. What happens if you don’t put your phone on airplane mode?. [online] Lonely Planet. Available at: https://www.lonelyplanet.com/articles/why-use-airplane-mode-flights
- Oyatogun, F., 2021. Why must you switch off your phone on a plane during takeoff and landing?. [online] Showmeonething.com. Available at: https://www.showmeonething.com/p/why-must-you-switch-off-your-phone?
- Leggett, T., 2021. 5G phones: How serious is the threat to US flights?. [online] BBC News. Available at: https://www.bbc.com/news/business-60042178
