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Explained: C-Band 5G frequency and how it can affect aircraft altimeters

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Explained: C-Band 5G frequency and how it can affect aircraft altimeters

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Major US wireless carriers are switching to C-Band 5G, which operates in a frequency that could potentially interfere with the frequency used by altimeters on airlines. Altimeters are devices that can tell how high above the ground the aircraft is flying. Altimeters are especially useful on a cloudy day or over mountainous terrain where visibility is limited. 

Explained: C-Band 5G frequency and how it can affect aircraft altimeters
In the ongoing standoff between airlines and wireless carriers over 5G rollout in the United States, US telecom major AT&T may have been the first to blink--albeit temporarily--followed by Verizon, but the problem reached our shores, so to speak, when Air India cancelled eight US-bound flights yesterday, with the country's aviation regulator, the Directorate General of Civil Aviation (DGCI), scrambling to find a solution.
A solution to what, exactly?
So, 5G is basically the fifth generation of mobile connectivity, and follows the first generation (GPRS), the second generation (EDGE), and the fourth generation (4G or LTE).  Currently, most countries in the world--including ours--are still on 4G; some have already made the jump to 5G, while others are about to.
Till last year, 5G was broadly deployed in the US in two frequencies. The first is the high-frequency millimetre wave (mmWave), which operates in the 28-39 Giga Hertz (GHz) frequency, which is considerably higher than 4G frequencies, which are typically between 700 and 2,500 Mega Hertz (MHz). Mobile internet speeds have been reported to touch 1Gbps in mmWave, but  a high-band tower can cover a radius of only a couple of kilometres and even tree leaves reportedly disrupt the coverage.


In contrast, a low-band (700MHz) tower can cover hundreds of square kilometres. But low-band 5G is essentially just a faster version of 4G; operating in the sub-1GHz frequency, it offers the widest coverage and speeds of around 1-2 times more than 4G.
So what's the problem now? 
The standoff in the US started recently when the two biggest wireless carriers in the country, AT&T and Verizon, switched to a new frequency to widen and improve 5G coverage. The new frequency, C-Band, hits the sweet spot in 5G frequencies, offering the widest coverage with the highest speeds possible.
The C-Band operates in the  3.7-3.98GHz frequency, which is close to the 4.2-4.4GHz frequency used by altimeters on airlines. Altimeters are devices that can tell how high above the ground the aircraft is flying. Altimeters are especially useful on a cloudy day or over mountainous terrain where visibility is limited.
Further, a C-Band tower has a coverage radius of a few square kilometres.
This has sparked off protests from the aviation industry, with airlines claiming  that deployment of C-Band 5G near airports could interfere with the flights' altimeters. Several airlines have asked "that 5G be implemented everywhere in the country except within the approximate 2 miles (3.2 km) of airport runways" at some key airports.
What will happen now?
On Tuesday, chief executives of major US airlines, in an alarmist letter to the Biden administration, claimed "airplane manufacturers have informed us that there are huge swaths of the operating fleet that may need to be indefinitely grounded".
In a nightmare scenario, flights will not be able to land or take off due to the presence of nearby 5G towers, or even the presence of a significant number of people inside airports using the C-Band 5G network, airlines said.


As per a Vox article, the United States' Federal Aviation Administration (FAA) said  on on January 16 that it had approved two altimeters used in many Airbus and Boeing airplanes, which cleared about 45 percent of the US commercial airline fleet to fly when these new 5G frequencies are turned on.
For now, flights from other countries are slowly resuming after the "ceasefire" in which At&T and Verizon agreed to defer the rollout of C-Band 5G near a few key airports. US transport secretary Pete Buttigieg is hard at work to untangle the problem, meanwhile.
The India scenario
At home, 5G spectrum auctions are expected to take place in April-May, with a tentative launch slated for August 15, 2022. While there is no clarity on the spectrum that will be up for grabs, most telecom providers in the country are testing their 5G capabilities on the 3.5GHz band. As one might expect, this has been red-flagged by the Indian aviation industry including the 6000-member Federation of Indian.
 
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