New high-speed mobile phone services have raised concerns about interference with aircraft operations, particularly when aircraft are landing at airports. The Federal Aviation Administration has assured Americans that most commercial flights are safe, and AT&T and Verizon have agreed to delay the installation of new cell phone antennas near airports for six months. However, the problem is not completely resolved.
Concerns began when the U.S. government auctioned off some C-band spectrum to wireless carriers in 2021 for $81 billion. The carrier uses the C-band spectrum to offer his 5G services at full speed, which is 10 times faster than 4G networks.
The C-band spectrum is close to the frequencies used by key electronics needed for aircraft to land safely. Here’s why it’s a problem:
maintain spectral order
Wireless signals are carried by radio waves. The radio spectrum ranges from 3 hertz to 3,000 gigahertz and is part of the electromagnetic spectrum. The portion of the radio spectrum that carries signals from phones and other wireless devices ranges from 20 kilohertz to 300 gigahertz.
Noise occurs when two wireless signals in the same area use the same frequency. This sound is heard when you are between two radio stations transmitting information using the same or similar frequency bands. The signal is jumbled, sometimes you hear one station, sometimes another, all mixed in with a healthy amount of noise.
Therefore, in the United States, the use of these frequency bands is restricted by the Federal Communications Commission so that wireless stations, wireless carriers, and other organizations are allocated “lanes” or frequency spectrum for use in an orderly manner. is strictly regulated.
radio waves are reflected on the ground
Modern airplanes use altimeters, which calculate the time it takes for a signal to reflect from the ground to determine the airplane’s altitude. These altimeters are an important part of the automatic landing system and are especially useful in low visibility conditions.
AP Photo/Rob Griffiths
Therefore, when the altimeter interprets the signal from the wireless carrier as a reflected signal from the ground, the altimeter determines that the ground is closer than it actually is and may prematurely lower the landing gear or perform other maneuvers necessary for landing. You may try to run it. aircraft. If interference with the radio carrier signal corrupts the altimeter’s radio signal and disrupts the signal, the altimeter may no longer be able to see the bounced signal and therefore have no idea how close the plane is to the ground.
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Airplanes and cell phone companies use different parts of the radio frequency spectrum. The problem is that airplane altimeters use a range of 4.2 to 4.4 gigahertz, whereas previously unused C-band spectrum recently sold to wireless carriers ranges from 3.7 to 3.98 gigahertz. That’s true. It turns out that the 0.22 gigahertz difference between the signals may not be enough to be completely confident that the cell phone carrier signal won’t be mistaken for the altimeter signal or corrupted.
AP Photo/Alastair Grant
Please avoid trouble for the time being.
The telecommunications industry claims that a gap of 0.22 gigahertz is sufficient and that no interference will occur. The airline industry is becoming more cautious. I believe that even though the risk is very small, the impact of a plane crash is very large.
Who is right? The chance of such interference occurring is very small, but in reality there is not much data to say that such interference will never occur. Whether there is interference depends on the altimeter receiver and its sensitivity. In my opinion, there is no way to guarantee that such stray interfering signals will not reach the altimeter.
If the altimeter can register stray signals as noise and filter them out, the altimeter will function properly. But updating aircraft altimeters costs a lot of money, and it’s unclear who will pay for it.
The FAA is testing altimeters and is working to develop a reliable altimeter in the near future. AT&T and Verizon have agreed not to install 5G transmitters and receivers near their 50 largest airports for six months while a solution is considered. This averted a major crisis in the short term, but it is not a permanent solution.
Additionally, local airlines and local airports remain at risk of interference.
