When Apache attack helicopters engaged the Medina division of the Iraqi Republican Guard during Operation Iraqi Freedom, pilot crews were forced to absorb some small arms fire and operate in dangerous proximity to enemy troops. Senior Army leaders described this combat scenario as driven primarily by a need to conduct a “targeting mission,” yet the Apaches encountered windy, sandstorm-type conditions which obscured pilots’ vision and made it difficult to maneuver in response to enemy fire. Regrettably, there were some U.S. casualties in the engagement.
Iraq is desert terrain, so the ground below was naturally flat, yet if visibility was in any way obscured by brown-out conditions, pilot crews operated a much higher risk of having a fatal collision with the ground during high-speed attack maneuvers.
Drones, fighter jets, helicopters and even missiles all rely upon radar altimeters to determine altitude, proximity to terrain and navigational accuracy. These instruments help them avoid potentially catastrophic collisions with the ground. Essentially, they are not only crucial to operational effectiveness, but also, of greater significance, when it comes to saving lives.
“Radio altimeters are vital below approximately 2,500 feet. At that point, only the altimeter can accurately measure a plane’s distance from the ground. If your aircraft, drone or even a missile thought it was at 2,000 feet but was only at 200 feet, you have a serious problem on your hands,” a senior government official told The National Interest.
However, despite the consequential role it plays when it comes to securing the successful operation of U.S. military aircraft in combat or homeland security missions, radar altimeter functionality may now be in serious jeopardy, according to senior U.S. government officials, who are expressing concern that a move by the Federal Communications Commission to reallocate a portion of the 3.7-4.2 GHz frequency band for use with 5G will interfere with and disrupt radar altimeter functionality.
“This spectrum will be auctioned to new licensees beginning in December 2020. The aviation industry noted in the FCC rulemaking process that deployment of 5G networks in this frequency band may introduce harmful radio frequency (RF) interference to radar altimeters currently operating in the globally-allocated 4.2-4.4 GHz aeronautical band,” an October 2020 RTCA essay on the subject states, called “Assessment of C-Band Mobile Telecommunications Interference Impact on Low Range Radar Altimeter Operations.”
While the FCC motivation could be inspired by an interest in expanding 5G into new markets across the United States and world, some lawmakers and government officials are seriously concerned about the dangers of interference with civilian, and particularly military, operations.
“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, and failures of these sensors can therefore lead to incidents with catastrophic results resulting in multiple fatalities,” the essay writes.
One senior government official explained that the interference complications could not only threaten functionality but also potentially cost billions of dollars to mitigate or repair.
As one senior government official with more than three decades experience in aviation said, “There will be accidents, property will be destroyed and innocent people are going to die.”
While military and commercial experts are fast making progress when it comes to better deconfliction of the spectrum and optimizing frequency allocations, the spectrum itself is a finite entity and there is a consistent need for more bandwidth to keep pace with rapid technological advances.
“The aviation industry has explained to the FCC that further study was needed to adequately characterize the performance of currently fielded radar altimeters operating in the presence of RF interference from future 5G networks in the 3.7—3.98 GHz band, as well as the risk of harmful interference and associated impacts to safe aviation operations, such that appropriate mitigations could be employed before such 5G networks begin operation,” the essay says.
“We simply must never take a chance with aviation safety full stop. Commercial interests can never be placed above safety,” the senior government official said.
Kris Osborn is the defense editor for the National Interest. Osborn previously served at the Pentagon as a Highly Qualified Expert with the Office of the Assistant Secretary of the Army—Acquisition, Logistics & Technology. Osborn has also worked as an anchor and on-air military specialist at national TV networks. He has appeared as a guest military expert on Fox News, MSNBC, The Military Channel, and The History Channel. He also has a Masters Degree in Comparative Literature from Columbia University.