So, here’s the FCC-FAA argument over 5G on which Inside Towers has reported extensively. The FAA and major U.S. airlines have taken issue with the FCC allowing the wireless carriers to use C-band frequencies in the 3.7-4.2 GHz range, especially that portion allocated for 5G use in the 3.7-3.98 GHz frequency range.
Let’s be clear. This portion of the C-band is the only 5G frequency range in contention. There are no other interference or related safety issues with low-band (600/700/800 MHz), lower mid-band (AWS, 3.45-3.55 GHz, CBRS 3.55-3.7 GHz) or millimeter-wave frequencies well above 10 GHz.
The FAA argues the 5G C-band frequencies are too close to those frequencies used by radio altimeters in aircraft of all types but especially commercial aircraft. Radio altimeters operate in the 4.2-4.4 GHz frequency range. This means there is a separation of 220 MHz between the high end of 5G frequencies at 3.98 GHz and the low end of the radio altimeter range at 4.2 GHz.
Even though it’s 5G, the C-band situation in Europe is completely different from the U.S. Most significantly, 5G services in Europe use a lower 3.4-3.8 GHz frequency range. This means there is 400 MHz or 1.8 times the separation from the high end of the European C-band range at 3.8 GHz and the low end of the radio altimeter range at 4.2 GHz. This larger separation significantly buffers the interference potential.
Besides frequency separation, interference can be minimized or eliminated with lower transmit power levels, restricting the placement of 5G cell sites close to airports and by tilting antennas downward to limit potential interference with aircraft flying at low levels.
In France, for instance, mobile operators must tilt antennas away from flight paths at 17 major French airports to minimize the risk of interference, as directed by France’s National Frequency Agency (ANFR). ANFR implemented these measures out of an abundance of caution. France’s civil aviation authority told CNN Business that “no event of 5G technology interfering with aircraft altimeters has been recorded by French operators.”
Nonetheless, the issue is safety. This proximity of frequencies, the FAA claims, could potentially hamper radar altimeter operation and affect the cockpit readings of how close to the ground an aircraft may be flying. Worse case, the pilots may not have accurate altitude readings during landings especially when visibility is reduced. Clearly this is a scenario to be avoided.
The FAA is so concerned about safe aircraft operation being affected by C-band interference that last week it issued nearly 1,500 orders limiting flight operations across the U.S. (see, FAA Seeks to Minimize Delays but Issues Almost 1,500 Flight Limits for 5G)
The unresolved debate between the FCC and the FAA has raised concerns among airlines outside the U.S. so much so that some international carriers have begun curtailing flights to the U.S. even though European airlines have not reported any of the FAA-cited problems in their home countries.
“The technical data received from EU manufacturers offers no conclusive evidence for immediate safety concerns at this time,” stated the European Union Aviation Safety Agency (EASA), according to a CNN Business report. “At this time, EASA is not aware of any in-service incidents caused by 5G interference,” added EASA, which oversees civil aviation in 31 European countries.
Similarly, the U.K.’s Civil Aviation Authority in a safety notice stated, “there have been no confirmed instances where 5G interference has resulted in aircraft system malfunction or unexpected behavior.”
Both AT&T and Verizon are most affected by these U.S. inter-agency machinations since they won the biggest blocks of C-band licenses. Still, both companies are cooperating by lowering the RF transmit power at cell sites near major airports, in some cases not activating a few cell sites at all, and by keeping full power 5G sites at a distance from flight paths. These accommodations are finite while both carriers give the governing bodies more time to sort through the issues.
By John Celentano, Inside Towers Business Editor