Image: US Coast Guard, Petty Officer John Masson

Blog Editor’s Note:

It was a dark and eerily calm night. The worst-case scenario for a helicopter rescue of someone from the water. On dark and stormy nights at least the pilots can at least see the waves. That night black water and black sky showed no horizon. As we descended toward the glassy surface it was impossible to tell where the air ended and the water began. Beep, beep, beep, – the radar altimeter warned we were less than 25 feet from hitting the surface. It was the difference between our saving the lives of five people in a life raft and losing our own lives in the attempt.

Radar altimeters are lifesavers in dozens of aviation applications from emergency helicopter operations to safe landings for passenger aircraft. Yet, in another Ligado-like move, the Federal Communications Commission has repurposed what had been spectrum set aside for low power space-based signals to make it available for higher power terrestrial 5G signals. And – surprise, surprise – the high power signals are going to disturb the neighbors. In this case lifesaving radar altimeters. 

Below is the press release from the Radio Telecommunication Commission, Aviation (RTCA) which has taken a long, close, thoughtful look at the radar altimeter issue. We are not sure the Federal Communications Commission has done the same. 

BTWIn case you missed our summary of the aviation GPS impact of the FCC’s Ligado decision, you can find it here.

Aviation Groups Call for Halt of FCC Spectrum Auction Affecting Radar Altimeters 

DECEMBER 7, 2020
Home / News / Aviation Groups Call for Halt of FCC Spectrum Auction Affecting Radar Altimeters

WASHINGTON, D.C., December 7, 2020 – Today, a group of 15 aviation associations sent a letter to the Federal Communications Commission (FCC) expressing concern over frequency spectrum relocation affecting radar altimeters, a critical flight safety tool. The group requested that the FCC suspend Auction 107, scheduled to begin December 8, which offers new flexible‐use overlay licenses for spectrum in the 3.7–3.98 GHz band, in order to resolve likely interference issues with radar altimeters prior to the auction.

“Since 2017, the aviation industry has consistently noted during the Federal Communications Commission rulemaking process that deployment of 5G networks in this frequency band may introduce harmful radio frequency interference to radar altimeters currently operating in the globally-allocated 4.2–4.4 GHz aeronautical band,” the group wrote. “Radar altimeters are deployed on tens of thousands of civil aircraft in the United States and worldwide to support several critical safety-of-life aircraft functions throughout multiple phases of flight. Radar altimeters are the only sensor onboard a civil aircraft which provides a direct measurement of the clearance height of the aircraft over the terrain or other obstacles.”

The group’s request to suspend the auction is rooted in findings from a RTCA study on the impact of C-band mobile telecommunications interference on low range radar altimeter operations. The study revealed that 5G telecommunications systems in the 3.7–3.98 GHz band will cause harmful interference to radar altimeters on all types of civil aircraft—including large commercial transport airplanes; business, regional, and general aviation airplanes; and both transport and general aviation helicopters.  Without appropriate mitigations, such interference could lead to catastrophic failures. The study was submitted to the FCC for consideration back in October and additional information was provided to the FCC today.

The aviation associations signing onto the letter to the FCC Commissioners include Aerospace Industries Association; Airborne Public Safety Association; Air Line Pilots Association, International; Aircraft Electronics Association; Aircraft Owners and Pilots Association; Airlines for America; Cargo Airline Association; Experimental Aircraft Association; General Aviation Manufacturers Association; Helicopter Association International; National Air Carrier Association; National Air Transportation Association; National Business Aviation Association; RTCA; and Regional Airline Association.