US airlines begin installing 5G C-band filter for radio altimeters on Airbus A320s

(Photo courtesy of Thales)

US airlines have begun installing a replacement radio altimeter for in-service Airbus A320 models that are currently equipped with altimeters susceptible to interference from C-band 5G wireless signals generated by networks recently deployed by AT&T and Verizon. Thales, the avionics maker based in Toulouse, France, has confirmed the start of installations of an upgraded version of its radio altimeters that will replace the older 5G C-band sensitive ERT 530.

A September 14 Update published on the Thales Aerospace brand’s LinkedIn page notes that 50 A320 aircraft operated by unnamed airlines have been equipped with the ERT530R. The A320 radio altimeter upgrade program for US-registered A320s is the result of the FAA’s June requirement for regional aircraft operators the agency identified as most susceptible to signal interference. 5G C-band wireless to install radio frequency filters by the end of the year.

“At this stage, Thales has received approximately 2,000 orders for its enhanced, 5G-immune radio altimeters,” Thales notes in its LinkedIn updates.

Thales has obtained a European technical standard order for the first time permission from EASA for the ERT530R in July. The ERT530R uses bandpass RF filtering, a technique that isolates signals in certain frequencies, in this case, those in the 4.2-4.4 GHz range used by aircraft radio altimeters. Signals occurring above and below this range, such as those from AT&T and Verizon’s 5G networks, are attenuated, according to an overview of how bandpass filters work published by Direct sciences.

Aircraft radio altimeters operate in the 4.2 to 4.4 GHz range, the lower half of which is in the C band, a frequency range of 3.7 to 4.2 GHz where the combination of the signal transmission and capacity is optimal. The 5G wireless networks operated by AT&T and Verizon are in the 3.7–3.98 GHz frequency range, near altimeters.

Under an agreement reached with the FAA in June, announced with the RF filter requirement, AT&T and Verizon are delaying switching on parts of their respective C-band 5G wireless networks until July 2023.

The A320s, like all Airbus aircraft models except the A380, are fitted with two radio altimeters which provide height information to the aircraft’s autopilot, autothrust, primary flight displays and weather radar, among other navigation systems, according to the 2011 article “Radio Altimeter Erroneous Values” published by two Airbus engineers.

Several American airlines contacted by International Avionics in August regarding the FAA’s 5G C-band radio frequency filter requirement declined to comment on individual in-service aircraft upgrade progress. Most relied on a statement provided by an Airlines for America representative.

“As the U.S. airline industry works to actively install required aircraft modifications, we remain in close communication with the federal government, telecommunications companies, manufacturers and other stakeholders to achieve our shared goal of work to safely implement additional 5G service, so that the United States remains a global leader in security and technology innovation,” an A4A representative said in a statement sent by email.

The FAA also declined to comment on progress in retrofitting specific aircraft models with radio frequency filters.

“The Brazilian safety regulator and the FAA have already approved retrofit kits for regional aircraft which make up the bulk of aircraft requiring retrofits by the end of 2022,” an agency representative wrote to Avionics. “I don’t have the exact number of aircraft that have been retrofitted, but the number is over 50 and we know that many kits are either in transit or already in the hands of operators.”

A Boeing representative said in a statement to Avionics last month that the company “is actively working with suppliers, regulators, airlines and telecommunications companies to ensure long-term stability and help ease operational restrictions where possible with the aim of promoting the safe coexistence of aviation and 5G environments for all models in the Boeing fleet.”

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