Avionics designer, developer and manufacturer FreeFlight Systems has launched the RA-4500 Mark II (MK II) radar altimeter (RadAlt) as an upgrade path for FreeFlight Systems RA-4000 and RA-4500 customers. The RA-4500 MK II upgrades existing RA-4000 and RA-4500 installation with a robust 5G mitigation solution.

With the Federal Communications Commission (FCC) approving the use of a previously reserved radio frequency (RF) spectrum in the lower C Band in support of 5G systems deployment, many currently fielded RadAlts, including the RA-4000 and RA-4500, have been found to be susceptible to incorrect altitude readings due to C Band 5G interference.

During recent testing, many currently fielded RadAlts from various manufacturers, including FreeFlight, were shown to be vulnerable to strong C Band 5G RF interference. While FreeFlight's new Terrain series RA-5500 and RA-6500 have been designed to mitigate C Band 5G interference, the previous RA-4000 and RA-4500 RadAlts were designed and certified between 2008 and 2009 before the effects of 5G interference were known.

“Our RA-4000 and RA-4500 units are currently safely supporting flight operations on over 5,000 aircraft worldwide,” says president Anthony Rios. “However, having foreseen the potential deployment of C Band 5G back in 2019, we understood that our customers would need a robust, clean sheet designed radar altimeter that would be tolerant to C Band 5G while being simple to install and cost-effective to upgrade from existing radar altimeters.”

For aircraft with existing RA-4000 and RA-4500 RadAlts, FreeFlight is introducing the RA-4500 MK II radar altimeter as a simple drop-in replacement that utilises the existing wiring, structural and antenna provisions already on the aircraft. This ensures operators can quickly address the risk of 5G interference and FAA Airworthiness Directives (ADs) with no modifications to existing aircraft provisions. This path for upgrade is available to all FreeFlight customers ranging from business aviation, general aviation, military and defence, uncrewed aviation and rotorcraft platforms.

“To address the restrictions imposed by the published FAA ADs, we recommend existing RA-4000 and RA-4500 customers to upgrade to the RA-4500 MK II to mitigate effects of 5G infrastructure to continued flight operations,” adds Rios. “As experts in radar altimetry and the 5G space, we will support our customers in navigating the AMOC submission process with data, expertise and collateral materials as needed in the process.”

The new Terrain Series RadAlts are now undergoing the testing required to support Alternative Method of Compliance (AMOC). The first round of formal testing has been completed with exceptional results, proving that its robust design can coexist with C Band 5G networks.

The testing, which employed industry-standard test setup, methodology and analysis, was used to determine interference tolerance of the RadAlts in terms of their protection radius or how close to 5G towers the RadAlt can get without being affected. The better the interference tolerance of the RadAlt, the smaller the protection radius around a given 5G antenna can be.

Based on the test results, the Terrain series demonstrated a protection radius of at least an order of magnitude better than one nm. This means that the new line of RadAlts, with its unique, patent-pending combination of a redesigned internal RF filtering circuitry and innovative Digital Signal Processing (DSP), provides industry-leading 5G interference mitigation compared to other in-service RadAlts.

“We set out to design the Terrain series to co-exist with C Band 5G networks from a clean sheet. Today, it is the only altimeter in the market that has been specifically designed for this,” says Rios. “We started working towards this design nearly two years ago and are proud to see the exceptional performance results. We now look forward to seeing the benefits to safety our radar altimeters will have for operators around the world.”

FreeFlight Systems will continue the testing of the Terrain series radar altimeters and improve performance as more refined AMOC methodologies emerge.

“Despite the exceptional performance, we do not want to stop here,” he continues. “The innovative design enables FreeFlight Systems to continue to refine the 5G interference performance of the Terrain series through software enhancements. Further improvements will be available to Terrain series customers as field loadable software updates, effectively future-proofing the radar altimeter for FAA minimum performance standards expected to evolve in the future.”

The Terrain series' Design Assurance Level (DAL) B criticality, dual-install compatibility, altitude measurement range of up to 2,500 ft and 55,000 ft service ceiling make it ideal for new or retrofit Part 29 rotorcraft and larger fixed-wing aircraft installations. The small footprint design means that it can easily be installed in place of legacy altimeters from various manufacturers.

For simplified retrofit installations, the Terrain series altimeters support existing antennas, cockpit displays and wiring provisions already installed on the aircraft. Further, to support a wide range of aircraft platforms across heavy rotorcraft, regional air transport, turboprops, business aviation and military segments, the Terrain series incorporates the latest ethernet connectivity standards for new platforms while retaining an analogue ARINC 552 interface for integration with legacy indicators and components. For additional display options, FreeFlight Systems offers the RAD45 standalone indicator which meets EASA AMC1 SPA.NVIS.110(b) guidelines.