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FreeFlight Systems unveils clean sheet radar altimeters designed to resist powerful 5G network interference

By Lisa Gordon | April 12, 2022

Estimated reading time 9 minutes, 5 seconds.

As consumers everywhere look forward to 5G service for its blazing fast streaming and surfing capabilities, the aviation industry is keeping a wary eye on how the technology will affect critical safety equipment.

To make way for the high-powered 5G network, the U.S. Federal Communications Commission (FCC) recently opened up a radio frequency spectrum that was previously reserved for lower-power units. This spectrum is very close to the operating frequency of radar altimeters, which provide critical altitude measurements to both manned and unmanned aircraft. 

As telecommunications companies encroach upon these previously reserved frequencies, stronger 5G signals can interfere with radar altimeter readings, degrading their performance and posing a significant safety hazard to all kinds of aircraft.

“Radar altimeters are not new; they have been in use for decades,” explained Anthony Rios, president of FreeFlight Systems. The Texas-based company manufactures aviation navigation instruments, including GPS receivers, automatic dependant surveillance – broadcast (ADS-B) receivers and radar altimeters. 

“When they were originally designed, there was an assumption that the frequencies below and above their operating frequency were protected. As a safety critical device, there was an expectation that nothing would encroach on those bands. However, some of the telephone companies are buying frequencies adjacent to radar altimeters. Their high-power transmitters are too close to radar altimeter frequencies, which were not designed to protect against this interference.”

Initially, to preserve aviation safety, telecommunication companies such as ATT and Verizon voluntarily restricted the rollout of 5G network, while the FAA limited flight operations in areas where there might be interference affecting critical flight regimes. There were steps taken to limit upward transmission and power around some airports. However, Rios said these voluntary restrictions are due to expire as early as May—and at that point, telecommunications companies could increase signal power, continue adding more antennas and potentially change their angles. The FAA is constantly updating its Notice to Air Missions (NOTAMs) to accommodate the additional antenna sites.

The situation has caused radar altimeter manufacturers to search for solutions. Many are adding filters to existing units that are designed to patch them through for the time being, although Rios referred to these as “Band-Aid solutions.”

The FAA has created an alternative means of compliance (AMOC), allowing operators with a certain type of filtered equipment to continue doing specific flight operations. Testing has revealed a minimum radius around 5G antennas where filtered radar altimeters will still provide accurate readings. For legacy radar altimeters, this radius could be as much as 3.5 to four nautical miles. 

Helicopters Impacted

While the FAA has largely protected runways and airports from the encroachment of 5G towers, they have not been able to do much for helipads.

“Imagine a dense urban area where helicopters operate all the time,” said Rios. “How do you provide protection from 5G signals? All of these operators will be restricted from operating there.”

He said 5G network signals will affect anyone who uses a radar altimeter, period.

“A radar altimeter is a safety critical device that will be more critical in certain operations, with limited visibility, IFR, at night, in rural areas, or any time the pilot cannot see out the window. The emergency evacuation segment, as well as police and fire, they have to go when called upon. For them, it’s most critical to be able to launch in all weather conditions.”

Rios said that while 5G has been rolled out relatively slowly so far, that will change in the coming months.

“5G is not widely deployed yet,” he noted. “The 5G environment we are in today is just starting to be deployed. Now, there are operating restrictions with 5G; but over time, we will see stronger restrictions in the urban areas. A lot of these AMOCs are dependent on the limited existing deployment. Filters might work today, but will they work tomorrow? It’s difficult to know.”

That’s why FreeFlight Systems has gone back to the drawing board with a clean sheet radar altimeter design that will provide better protection from 5G signal interference.

The origin of its new Terrain Series goes back to 2019, when the company realized the problems posed by 5G.

“That’s really what differentiates our offering,” said Rios. “The engineering team looked at filters and realized they wouldn’t cut it. The main principle of these new radar altimeters is to introduce digital signal processing, which allows us to filter very precise frequencies. Today, we are the only manufacturer that has a purpose-built design around 5G.”

The Terrain Series includes three models: the RA-6500 is a dual installation model providing for two units on a single larger aircraft; the RA-5500 employs the same technology but for a single unit installation or UAV offering; and the RA-4500 MK II is an affordable drop-in replacement for the company’s existing RA-4500 FreeFlight radar altimeter.

The Terrain Series is also designed to provide a simple upgrade solution for other popular but older radar altimeters, such as Honeywell’s KRA-405B and RT-300 models.

Rios said all three models in the Terrain Series family can be installed in all types of aircraft, from business jets to regional jets to Part 29 helicopters.

“The Terrain Series protection range is 1/10 of a nautical mile, so you can operate a helicopter within 600 feet of a 5G antenna and still have the assurance it’s safe,” he said. 

Currently, the units are undergoing the necessary testing to AMOC standards. Rios said FreeFlight Systems expects to receive Technical Standard Orders (TSO) performance approvals by the end of April, with product shipments beginning shortly afterwards. Currently, the company is taking orders.

Rios, who attended the recent HAI Heli-Expo 2022 tradeshow in Dallas, Texas, said he was surprised by the seemingly low awareness about the 5G network and its impact on radar altimeter operations.

“Of all the people I spoke to, everyone was a bit surprised and maybe caught off guard,” he said. “Since the show, we’ve had more call-backs.” 

In particular, he reported that urban air mobility (UAM) and unmanned aerial vehicle (UAV) operations are very interested in Terrain Series radar altimeters, due to their operations in densely populated areas with intense 5G signal interference.

“In this world of global supply chain problems, we are prioritizing our materials to build as many radar altimeters as possible,” concluded Rios. “We are predicting a firestorm where people become aware and the FAA goes on to impose more restrictions. We are doing our best to educate our customers now.” 

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