FreeFlight Readies 5G-interference-resistent Radar Altimeters

 - March 30, 2022, 10:05 AM
(Photo: Matt Thurber)

FreeFlight Systems is in the final stages of obtaining FAA Technical Standard Order (TSO) approval for its Terrain series 5G-interference-resistant radar altimeters. The company plans to submit all required paperwork for the TSO in early April, and approval should follow shortly.

At the Aircraft Electronics Association convention this week in New Orleans, FreeFlight president Tony Rios noted that the Terrain series radar altimeters provide an “AMOC radius” of 0.1 nm or better. Most existing radar altimeters, including FreeFlight’s earlier products, are subject to 5G cellular network C-band interference at 2 nm or more distance from the transmitting 5G antenna. “Outside of this radius, [radar altimeters] will not be affected,” the company explained. “Inside, it may not be available or is giving undetected, erroneous altitude readings.”

The new FreeFlight RA-4500 Mk II radar altimeter replaces the existing 4000/4500 units installed in many airplanes and helicopters. It will be a form, fit, and function replacement, under a service bulletin issued by the aircraft manufacturer, so no supplemental type certificate (STC) will be required. “Then it is 5G-resistant,” said Shane LaPlante, v-p of sales and marketing. “That addresses the existing market.”

The RA-5500 and RA-6500 are designed to replace Honeywell KRA-405B and Garmin GRA 5500 radar altimeters. The FreeFlight RA-5500 is for installations where only a single radar altimeter is required, while the RA-6500 is for dual-unit installations. The RA-6500 can be installed as a single unit, with a second added later, he explained. Both the RA-5500 and RA-6500 are designed with a smaller footprint than the radar altimeters they replace as well as the ability to connect to the existing wiring and antennas for easier installation. STCs will be required for the RA-5500 and RA-6500, and FreeFlight plans to work with installers on these, including approved model list STCs that would cover multiple aircraft models. To further simplify installations, an analog card for the Terrain series radar altimeter is available to allow retention of older analog displays so they don’t need to be updated to a digital display right away.

FreeFlight’s Terrain series radar altimeters were designed to mitigate 5G interference using digital signal processing (DSP) technology to filter out unwanted signals. “All the filtering is done digitally,” LaPlante explained. Some proposals to fix this problem for older radar altimeters envision the use of band-pass filters, he said, “but that doesn’t address in-band spurious signals.” The DSPs in the Terrain series radar altimeters allow FreeFlight engineers to filter all of the “bad” signals, including spurious signals, and if and when those signals change, FreeFlight can simply adjust the unit’s susceptibility via software updates.

Although full deployment of C-band 5G networks in the U.S. has not yet occurred, “Overall industry awareness [of the 5G interference issue] remains quite low,” according to FreeFlight Systems, “especially in the rotorcraft community. One thing that we don’t think people realize is that the failure modes of [radar altimeters] in the 5G environment cannot be characterized—the equipment simply was not designed to operate in these conditions. Testing has shown across the industry (including our own testing ) that an affected altimeter is as likely to give wrong altitude information as it is to give non-computed data or a flagged fault condition. This is a risk we have never seen before as a widespread problem in aviation, and it must be taken seriously.”