(Reuters) – The chief executives of major U.S. passenger and cargo airlines have warned of a “catastrophic” aviation crisis this week as AT&T (NYSE:) and Verizon (NYSE:) deploy new 5G services.

The new C band 5G service, which will begin Wednesday morning, could make a large number of American aircraft inoperable. This would cause chaos on U.S. flight routes and possibly stranding thousands of Americans abroad.

The background of the dispute is as follows:

WHAT HAPPENED?

For approximately $80 Billion, the United States offered mid-range 5G bandwidth for mobile phones companies to auction in 2021. It was located in the 3.7-3.98GHz spectrum range known as the C Band.

WHY IS THIS A PROBLEM

The U.S. Federal Aviation Administration (FAA) has warned that the new 5G technology could interfere with instruments such as altimeters, which measure how far above the ground an airplane is travelling.Altimeters operate in the 4.2-4.4 GHz range and the concern is that the auctioned frequencies sit too close to this range.

Altitude and wind shear are not the only things that altimeters can readout.

Scott Kirby, CEO of United Airlines (NYSE:), stated last month that the FAA’s 5G directives for radio altimeters would prohibit the use at 40 of America’s largest airports.

U.S. airlines warned that the directives could cause disruptions of up to 4% in daily flights.

Kirby explained that this could result in major U.S. Airports having to use visual approaches when there is bad weather, clouds or heavy smog.

WHAT DIFFERENCE DO THE FREQUENCY MAINTAIN?

A faster service will run the higher the frequency of the spectrum. Operators want to use higher frequencies in 5G to maximize their potential.

While some of the spectrum in the C bands was used to transmit satellite radio, the transition from 5G will see much more traffic.

What do the TELECOMS COMPANIES SELL?

Verizon and AT&T have argued that C band 5G has been deployed in about 40 other countries without aviation interference issues.

In order to minimize interference risks, the two countries have agreed for 50 United States airports to be placed in buffer zones, similar to France’s.

WHY CAN’T THIS ISSUE BE FIXED ELSEWHERE?

2019 was a year in which the European Union set the standards for the mid-range frequency of 5G in the 3.4-3.8 GHz band. This is a lower frequency that the service to be launched in the United States. It has already been used in several of the 27 EU member countries without any problems.

European Union Aviation Safety Agency, which supervises 31 countries, stated that the problem was only applicable to U.S. aviation space on December 17. It stated that “At the moment, there is no danger of unsafe interference in Europe.”

FAA officials noted that France is using spectrum (3.6-3.8 GHz, compared to the spectrum (42.2-4.4 GHz) for altimeters in the United States. France also uses a lower power level than is allowed in the United States for 5G.

Verizon stated that it would not be using spectrum in the lower band over several years.

South Korea’s 5G mobile frequency band is between 3.42 and 3.7 GHz. There has not been any interference reported with radio waves since April 2019, when 5G was commercialized.

At the moment, there are 5G wireless communication stations near airports. However, no problems have been reported.

CTIA, an American wireless trade organization, stated that nearly 40 countries in Europe and Asia have now adopted the C band to support 5G. There are no reports of any adverse effects on radio operators operating in the same international 4.2-4.4GHz spectrum.