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5G Hardened Radar Altimeters Emerge

An answer to the boogieman that is next-gen cellular.

FreeFlight Systems
Photo courtesy of FreeFlight Systems

The negative impacts to aviation of the implementation of 5G cellular towers starting late last year and in earnest early this year is news to no one. Chief though not unique on that list of affected aircraft electronics is the radar altimeter, which (mostly) larger planes, including just about all commercial and large business jets, use for precision approach and terrain warning purposes.

Before 5G cellular service was formally launched back in January, the FAA took measures to protect “big birds” using radar altimeters near large airports from potential 5G interference. The agency negotiated with the Federal Communications Commission for reduced power output of 5G antennas and created protected zones around major airports where mostly commercial aircraft will be making low visibility landing attempts in poor weather. Such operations, obviously, depend on the performance of the radar altimeter for precise and reliable awareness of altitude down to minimums. Notably, the FAA issued an AD in December 2021 specifying that NOTAMs will be issued at certain airports where radar altimeter performance has been verified as “unreliable,” thus prohibiting procedures that rely on it.

What about GA? Many of us operate fixed- and rotary-wing aircraft at small and mid-sized US airports probably never considered for a 5G protected zone during negotiations at the federal level. Our radar altimeters back up the glideslope on a precision approach and can feed an on-board terrain awareness and warning system (TAWS) with its all-important data feed.

Enter the market for 5G-friendly radar altimeters, such as units rolled out recently by FreeFlight Systems. These altimeters are like ancestor units except for the addition of a “unique combination of internal filtering and Digital Signal Processing technology that can tolerate out-of-band 5G interference as well as other RF interferences,” according to the company. That “out-of-band 5G” reference is a hat-tip to the fact that 5G cellular frequencies and radar altimeter frequencies are adjacent on the spectrum, not identical. This closeness is part of the reason such a debate has raged over the technology; interference has always been a risk, but not a certainty.

The FreeFlight RA-5500 is a new dual-antenna unit specifically developed for GA applications – including the emerging eVTOL market – and specifies “5G robustness” to up to 0.2 nautical miles. There is also a “Mk II” upgrade version of legacy Model 4000 and 4500 units available, with specific addition of the 5G hardening features.

This development doesn’t address the question of why owners and operators of radar altimeter-equipped aircraft should have to buy expensive new equipment to replace previously perfectly functional existing gear with no contribution from the companies that implemented 5G.

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