"*chii-chii-chi-tii-shii-buuuu*" that was the incoherent audible interference I heard on the sound system in my church while the choir was ministering. As a member of the technical unit, I quickly rushed to the sound system to know what could have caused the audible interference interrupting the glorious choir ministration. Alas!!! there were many smart phones charging in an electrical extension near the sound system(do not blame the innocent church attendants charging their phones_ blackout is a regular thing in my geographical location).
What should I do? that was the question that crossed my mind with the speed of light. And not just what to do, but what would immediately attenuate the audible interference already causing catastrophe to the ears of the able audience(church members) listening to the song.

My subconscious mind transmitted a good solution to my conscious mind; what was the solution? switch all the active phone to **airplane mode**. I took action even faster than flash or superman, I applied the solution and the audible interference attenuated immediately. All this action happened in less than a minute_ oh how speedy the subconscious mind and the brain(conscious mind communicate).  **Human would operate faster and more accurately than computers if humans could trust their subconscious minds and train it to do so**

The question you might be asking yourself now is "**why would smart phone or computer  cause audible interference in sound system**". Before any answer to your question let me explain what airplane mode is.
<h2>What Is Airplane Mode</h2>Airplane mode is a function included in smart phones and computers that allow user suspend **radio frequency signal transmission**<sub>more on this later</sub> by the smart phone or computer and other similar electronic devices.
<div class="pull-right"><img src="https://s6.postimg.cc/mgpntdbb5/airplane_modee.png"><center><br><sub>Cell tower. Image credits:<a href="https://creativecommons.org/">Creative Commons Public Domain</a> Wikimedia, <a href="https://en.wikipedia.org/wiki/File:Nexus5Android4.4.2inAirplanemode.png">Link]</a></sub></center></div>
Once user switches to airplane mode, calls, text messaging, cellular data, wifi, hotspot, bluetooth and all wireless connections stop propagating. I still remember playing music with my android phone via bluetooth connected to a Bluetooth speaker. As i switched to airplane mode, the speaker echoed "*Bluetooth disconnected, bluetooth connecting please wait*". I checked my android smart phone and observed that the Bluetooth automatically turned off as I switched to airplane mode.
Other names for airplane mode include offline mode, flight mode, aeroplane  mode and standalone mode.

<h3>What Is Radio Frequency Signal Transmission?</h3> To define this term, we will look at it in two facet
* Radio Frequency: It is an alternating  current(waves)  which its frequency is between the bandwidth of frequency used in radio. This bandwidth ranges from 20KHz to 300GHz as seen in most radio receiver
* Signal transmission is the process of propagating digital or analogue information from one point to another

So, radio frequency signal transmission is the process of propagating signals which its frequency is between the bandwidth of the frequency used in radio communication.
<h3>Why Do Smart Phones Cause Interference In Amplifiers and Other Sound Systems</h3>If you have ever kept your phone near a woofer, home theater or even radio receiver, you would be familiar with the audible interference some seconds before your phone rings or messages delivers. **What causes this phenomenon?**

Sound sytems(radio receiver, power amplifiers, wireless microphones) works wirelessly and wireless signals can be corrupted by noise.  Signals are always in the air but  any signal decoder selects the signal that is encoded for it, decode it and transform the encoded information to what humans can understand.  For lucid understanding, let me give an illustration:
>Assuming two classes in a close range in a primary school( class A and class B) having two differentiate teachers(teacher A and teacher B). Teacher A asked class A to repeat after him as he reads letters of the English Alphabet and teacher B also told class B  to repeat after him as he reads numbers 1-100 The both classes started as instructed<sub>both teachers are reading aloud</sub>. With time some pupils in class A might start repeating what teacher B is reading(numbers 1-100) instead of English alphabets.  That is simple confusion, but the number of pupils repeating the right thing would be higher.
<div class="pull-right"><img src="https://s6.postimg.cc/roaqy0mtd/cell_tower_use.jpg"/><center><br><sub>Cell tower. Image credits:<a href="https://creativecommons.org/">Creative commons attribution 3.0</a> Wikimedia, <a href="https://commons.wikimedia.org/wiki/File:Top_of_cell_tower_located_on_Sexton_Mountain_-_Beaverton,_Oregon.JPG">Link]</a></sub></center></div>

Similar thing happens in sound systems, when a smart phone in close range is  communicating with cell tower, it sends and receives digital wireless(radio) signals to/from the tower and at the same time, the wireless microphone is sending signal to the power amplifier in church. In some instant, the power amplifier will mistake signals from the smart phone as that from the wireless microphone_this is called **Signal corruption** in sound Engineering. This corrupted signal received by the power amplifier is sent to the speaker, that is the reason the *chiii-chiii-shii-buuu-diit* inchorent audible interference is heard in speakers.
<h3>What Will Happen in An Aeroplane If Smart Phones are Not Switched To Airplane Mode</h3>   
> In a revised review in October 2013, the United States Federal Aviation Administration (FAA) made a recommendation on the use of electronic devices in "airplane mode"—cellular telephony is disabled, while Wi-Fi may be used if the carrier offers it. Short-range transmission such as Bluetooth is always permissible. The statement cites the common practice of aircraft operators whose aircraft can tolerate use of these personal electronic devices, but use may still be prohibited on some models of aircraft<sub>[ref](https://en.wikipedia.org/wiki/Airplane_mode)</sub>

Assuming we are inside an aeroplane and someone has his/her smart phone active, the pilots would here an audible interference  in their headset whenever a text wants to deliver or when cellular data is turned on because of the smart phone communication with the network tower/mask.  Aeroplane's digital sound system also work with wireless(radio) connections, so it can be corrupted. Although for international flight flying above ten thousand feet, smart phones cannot communicate with cell tower 
<h3>Reasons You Should Switch to Airplane Mode</h3> It is not only in an airplane you should switch to airplane mode, there are other reasons as below:
1. For faster charging
2. For stable network: if your phone's network service is fluctuation, you can turn to airplane mode for some seconds
3. To avoid audible interference when in a close range to any audio system

<h4>Conclusion</h4>You have learnt why smart phones cause audible interference and how to avoid this.  We can avoid audible interference by switching to airplane mode or keeping smart phone far away from sound systems. whenever you want to board an airplane, kindly switch to airplane mode to avoid audible inference in the pilot's headset, this would lead to a safe fly.

Thanks for your ample time, I remain your brethren @ikchris


<h4>References</h4> Knowledge comes from somewhere and no man is an island of knowledge. Below are the links to what I studied to understand airplane mode and why smart phones causes audible interference in audio systems 
* [What is airplane mode](https://www.quora.com/What-is-airplane-mode)
* [Transmission and telecommunication](https://en.wikipedia.org/wiki/Transmission_(telecommunications))
* [Why do smart phones cause audible interfernece](https://www.scientificamerican.com/article/experts-cell-phone-screeching/)
* [Aviation Communication](https://en.wikipedia.org/wiki/Aviation_communication)
* [Radio](https://en.wikipedia.org/wiki/Radio)

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