The US Federal Aviation Administration (FAA) restricted the use of radio altimeters in some locations, the latest move in an ongoing spat with mobile operators over planned deployments of 5G in C-Band spectrum.

Restrictions were part of a series of FAA directives which could also see some flights blocked completely, as the regulator and US aviation industry turn the screw on operators regarding potential interference from 5G services in the C-Band.

Radio altimeters use spectrum in the 4.2GHz to 4.4GHz band. AT&T and Verizon plan to launch services using C-Band n77, which spans 3.3GHz to 4.2GHz.

The operators are on the brink of initial launches in the 3.7GHz to 3.98GHz range, after twice delaying the move due to concerns over interference with the altimeters.

AT&T and Verizon agreed to establish buffers around a host of airports to help allay the concerns.

Some operators of medical helicopters expect to be impacted by the latest FAA directives, unless aircraft manufacturers can show radio altimeters will not be adversely impacted by 5G.

A number of the notices issued by the FAA call on pilots to use “approved alternative methods of compliance due to 5G C-Band interference”, suggesting flights can proceed if the altimeters are not used.

Aviation Week reported the Helicopter Association International (HAI) called for mobile operators to mitigate 5G transmissions beyond the nation’s busiest airports, warning of a potentially devastating impact on public safety.

Mobile industry executives have pointed to France as an example of a country in which 5G in the C-Band and aviation safely coexist, with the FAA authorising US flights to the nation.

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