FAA says it wants airlines to replace radio altimeters facing interference with 5G C-band

Back in April 2021 the FCC auctioned off a new cellular frequency range for use with the new 5G cellular technology, this frequency range is called C-band. However, neither the FCC nor the FAA checked to see if this new frequency wouldn’t interfere with existing aircraft radio altimeters. They assumed it would not since they are different frequency ranges; however, since these frequency ranges sit very close together on the spectrum, many aircraft’s radio altimeters receive mask produced interference with the C-band frequencies, this causes radio altimeters installed on aircraft to produce incorrect readings.

AT&T and Verizon both agreed on Jan. 18 to delay switching on about 500 5G C-band antennas near key airports until July 5.

The FAA conducted a study aimed at finding out which aircraft/models of radio altimeters were prone to interference/inaccurate readings, the agency started work on a fix for this issue a couple of months ago. However, FAA administrator Steve Dickson said that the fix is not fully reliable and while it is a good stop gap, they should work on a more permanent solution to the issue. Dickson previously said that the FAA was working with radio altimeter manufacturers, cellular service providers and the RTCA to develop new radio altimeter standards, and that they hoped to settle on these new standards by early next year.

The FAA has been holding daily meetings with AT&T and Verizon that it said had “enabled us to closely tailor the areas requiring mitigation while aviation stakeholders take the necessary steps to retrofit existing radio altimeters with antenna filters.”.

Transportation Secretary Pete Buttigieg has been holding at least weekly meetings on the issue and has told Congress that they were making progress but that it wouldn’t be completely resolved by this summer.

The FAA will be holding a meeting on Wednesday with telecom and airline industry officials, it wants to use the meeting to establish an achievable timeframe to retrofit/replace the radar altimeters which have not been cleared, it will also look at what will happen after July 5 and said that there would be “changes to U.S. national airspace operating environment as a result of future 5G C-band deployment in the coming months.”. The meeting will also include a discussion on prioritizing retrofits with antenna filters which mitigate potential interference from 5G, officials said these filters are currently in production and are able to be retrofitted onto existing radio altimeters, and that a key question was how to determine which aircraft are most at risk of interference from C-band and should therefore get retrofitted with these first.

Source: Aviation Weekly News