Electromagnetic Interference: The Reason You Can’t Use Your Phone on Aircrafts
Electric fields can be produced by the voltages, and magnetic fields can be produced by electron flows. Combining both the electrical field and magnetic field will result in electromagnetic fields (EMI). Even though it is true that electromagnetic interference will not necessarily to bring down an aircraft from the sky, theoretically, there are potential risks and concerns the EMI can create a problem
Have you ever wondered that every time when you take a flight, why would the flight attendants ask you to turn off your cell phone and other electronic devices? Or have you ever raised the question that is it even possible to take down a ninety million airplane by your forty dollars IPod Shuffle? It will not surprise me if you asked any question like that. It is very common today that cell phones are banned during a flight. In the United States, the Federal Aviation Administration (FAA) prohibited the usage of cell phones and other passenger electronic devices on the aircrafts. Turkish Airline’s announcement states straight forwardly that “Mobile phones interfere with the flight instruments and have a negative effect on flight safety.”  Even more, some Chinese airlines prohibit all electronic devices during the flight. Today, most of the airlines around the world have similar regulations. Even the most loosely aviation regulations include banning the usage of electronic devices during take-off and landing. Most of people have a sense that using cell phones and Wi-Fi in airplane is somehow dangerous, but they don’t know why. The most common view today for banning electronic devices during takeoff and landing is these devices may produce electromagnetic interference that interfere with the aircrafts’ navigation and communication systems, and therefore risks the plane and passengers in great danger. In order to uncover more about how cell phones and other electronic devices will “messed up those giant steel birds”, at first we have to know what electromagnetic interference (EMI) is.
What is Electromagnetic Interference?
Imagine that you are working or studying in a quiet room, but suddenly, somebody turned on a vacuum cleaner. The sound that the vacuum cleaner makes is so loud that you cannot even focus on your work. This is an example very similar to the electromagnetic interference. In high school or college physics, students learn that electric fields can be produced by the voltages, and magnetic fields can be produced by electron flows. Combining both the electrical field and magnetic field will result in electromagnetic fields. EMI happens when the signals of electromagnetic fields temporarily interfere with other devices that are planned to be used .
Figure : Example of EMI on TV antenna system
Even though, for some people, EMI seem to be a professional term that only applies in the relevant fields, it actually exist surrounding our lives. Generally, there are two sources to cause an electromagnetic interference. The first one is electromagnetic radiation, a fundamental phenomenon that relates to the electromagnetic field, which is produced by moving charges. Electromagnetic radiation are generated by outside sources can interrupt or degrade the performance of an electrical circuit. A classic example of EMI by electromagnetic radiation in our daily lives is when we put our cell phones or laptops close to a radio that has been turned on, we often hear continuous “beep” noises from the radio’s speaker. That is because the electromagnetic fields of our cell phones or laptops interfere with the radio circuits. The second cause to generate EMI is electromagnetic induction, which occurs when magnetic field is varying. Sometimes, EMI occurs on our TV antenna systems (see Fig. 1) . In this case, it probably means that the TV signals are being distorted due to electromagnetic induction.
Figure :Cross-section through a coaxial cable showing shielding and other layers
Today, one major technique to reduce electromagnetic interference in a circuit is adding shields on electronic devices. Taking coaxial cable (see Fig. 2) as an example, the center core of the cable is formed by conducting material . Around the core, there is a layer of insulated covers to block external electric fields. This shielding technique is often known as Faraday Cage. The amount of electromagnetic interference reduction is depends on the material and its thickness, the size of shielded volume, and the frequency of the electric field. However, when we deal with EMI on airplanes, apparently this technique is not that promising because it is impossible to shield every part of the airplanes, and moreover their navigation and communication systems has to be exposed to receive radio frequencies from the outside. Thus, if the current technology cannot solve the EMI problem, then we should examine what risk that EMI will bring to the aircraft?
Can Your Cell Phone Really Bring down a plane?
As the question has been raised previously: is it even possible to take down a ninety million dollar aircraft from the sky by using forty dollar IPod Shuffle? The answer is a no. If any electronic device could do this much of damage, FAA or any other aviation related organization would prohibit consumers to carry electronic devices on board. In fact, according to a recent CNN news report, so far there is no such an event suggested that “electromagnetic interference from a portable electronic device brought down a commercial plane or was a contributing factor in an accident.” In addition, based on a survey by the Consumer Electronic Association, about one-third of airplane passengers admitted that they has left their electronic devices on during a flight in the last year . Giving a quick glance on these facts, it seems like if you do not follow the rules that flight attendants tell you, there is no big deal. The real reason that cell phones are impossible to bring down airplanes is because aircrafts control systems today are fully installed within the planes and absolutely shielded to keep outside signals away . However, even though it is true that electromagnetic interference will not necessarily to bring down an aircraft from the sky, theoretically, there are potential risks and concerns the EMI can create a problem. Thus the attitude of EMI will not affect aircrafts is wrong.
How EMI can affect aircrafts?
Unlike the well protected aircrafts control systems, aircrafts navigation systems are especially vulnerable. There are two reason for this: one is some parts of navigation systems are designed to detect and act on outside signals. The other reason that navigation systems are vulnerable is because radio based systems are very sensitive to even low level of interference . Therefore, electromagnetic interference to the navigation may potentially, although rare, affect aircrafts to deviate from the correct course or raise pilots’ operation difficulties during critical phase of flying (take-off and landing).
Aircrafts communication systems are also exposed to the outside signal by the similar way if the aircraft is under a serious EMI environment. Pilots communicate to the ground control, report the planes positions to the air traffic control, and collect weather information with all sorts of radio frequencies and different types of radars. If a consumer has his or her cell phone turned on, and the frequencies it transmitted overlaps with any frequencies that aircrafts are used, false message could be sent or received, which is hazardous to commercial aviation .
Nowadays, although scientists and engineers have proved in theory, electronic devices such as cell phones and laptops are potential sources to cause EMI in aircrafts, there is still no clear statistics showing what electronic devices will surely dangerous a commercial flight due to electromagnetic interference. It is also impossible for flight attendants to check or scan every consumer’s electronic devices before taking off. Therefore, the world consensus on making regulations to ban electronic devices in airplanes are based on the principle “better safe than sorry”.
Engineers are now seeking the solutions for EMI.
Figure : Working diagram of Pico cell
Just like the report that CNN news addressed in the end, “technology is creating a problem, and technology is solving the problem.” In Europe, some regulations and technologies have allow customers to use their phones in some limited commercial flights. On the other hand, facing the pressure of competition, many other airlines in the world is moving toward to seek new technologies to eliminate the barrier of EMI. In 2011, Emirates Airline start to provide Wi-Fi access on its A380. Recently, Emirates OnAir system allows passengers to use their own cell phones during the flight. Some American airlines now are also preparing to introduce new technologies to allow their passengers using cell phones in air and now waiting for permissions. Flights carry an equipment called Pico cell (see Fig. 3), a small cellular base station that can communicate send cell phones frequencies in the aircrafts to satellites or ground stations . However, the cost of using this on board calling service will be higher and the transmission speed will be lower. The cover range of Pico cell network is also small, but is enough to provide services on airplanes. Another company AeroMobile also provides on-board cellphone services on commercial flights. Its equipment can be installed while the planes are in manufacturing or in later upgrading. Currently there are sixteen airlines are using AeroMobile services. AeroMobile has its own cellular operator, which cell phone calls will be routed through satellites to the ground. In addition, AeroMobile will have an EMI screen system to keep mobile phones and other electronic devices from trying to contact with the ground-based networks. It is so far the best on-board cellphone services provider, and handling EMI issue well in its operation.
Electromagnetic interference is a usual phenomenon in physics world. Relating it to aviation, it can bring problems to both pilots and passengers. People today have realized it is time to invent some new technologies to deal with these problems. We have reasons to believe, in the near future, the problem of electromagnetic interference in aircrafts will be overcome by human’s wisdom. However, before we have fully solved this issue, we still need to pay attention on it. During a flight, the interference by electromagnetic field on the aircrafts instruments may be small, but the consequences can be high.
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