Until Flight Tests Begin, The Air Force Knows Little About 5G Interference and It’s Saying Less

Beyond citing no instances in which its operations have been affected by C-band 5G signals thus far, the U.S. Air Force remains mum on the impact of the new service. It may say more once government 5G flight testing begins – three months after the initial rollout was to have begun – in February but for now the service seems to have implicitly closed ranks on 5G commentary.

A day after C-band 5G service commenced, I asked the Air Force a series of questions about potential interference with the radar altimeters and avionics its aircraft use including what proportion of its overall fleet is potentially vulnerable to C-band interference, how many of its bases/joint bases had exposure to C-band 5G, and why the service had done no flight testing or significant analysis prior to the rollout.

A spokesperson for the Secretary of the Air Force (SAF PA) declined to answer with any specifics, instead affirming that DoD “is working closely with other stakeholders to keep our people apprised of FAA advisories, directives, and policies with regard to 5G implementation within national airspace.”

The Air Force is also participating in 5G C-band bench and live flight testing over the next several months as part of the Joint Interagency Five G Radar Altimeter Interference (JI-FRAI), an OSD Joint Test and Evaluation funded quick reaction test (QRT).

Describing the upcoming events as a “quick reaction test” says a lot about the Pentagon’s preparedness for the advent of C-band 5G.

In the years preceding the planned start of C-band 5G in December 2021, DoD remained largely silent on any impact of the use of 3.7–3.98 GHz frequencies for commercial telecommunications even as the Radio Technical Commission for Aeronautics (RTCA), released a report in 2020 on the risks of C-band interference with radar altimeter operation on nearby 4.2-.4.4 GHz spectrum.

In August of 2020, observers pointed out that the spectrum which DoD had released for auction to the telecoms was actually closer to avionics C-band than other frequencies — including a huge block of 3.1GHz to 3.45GHz spectrum — which DoD still holds.

The forthcoming joint flight testing was funded by the Pentagon, FAA and DHS in April of last year but there was apparently no urgency to get on with it with prior to turning on the lights for 5G service.

Lt. Col. Dylan McDermott, head of DoD’s Aviation Cyber Initiative, co-chaired with the FAA and Department of Homeland Security, told Breaking Defense that while the upcoming JI-FRAI flight tests will inform the services “what individual radar altimeters will or will not do in the presence of 5G,” the test team would not be offering mitigation recommendations after the trials conclude this summer.

The lack of understanding of potential interference and its impact on operations of Air Force airlifters, tankers, fighters, helicopters and special operations aircraft might have been expected to impel the service to ask for the same sort of suspension of C-band signals broadcasting near runways that the telecoms voluntarily agreed to for civilian airports on Wednesday. But SAF PA said Thursday that it was “not aware of suspensions near AFBs”, referring me instead to the telecoms.

A query on whether it has suspended C-band signals broadcasts near Air Force bases or Joint bases used by the Air Force was addressed by AT&T. Company spokesman, Alex Byers, responded with news that of the 46 markets where the telecom has initiated 5G C-band, it has deferred deployment at just one military air base, Naval Air Station Jacksonville, Florida.

Verizon did not respond to questions, leaving open the possibility that it may have suspended C-band broadcasts at locations near Air Force installations. Looking over the FAA’s NOTAM search page suggests a chance that there may be some C-band interference near Dover, AFB in Delaware. A NOTAM for DOV (Dover AFB) specifies the following;

“DOV AD AP RDO ALTIMETER UNREL. AUTOLAND, HUD TO TOUCHDOWN, ENHANCED FLT VISION SYSTEMS TO TOUCHDOWN, HEL OPS REQUIRING RDO ALTIMETER DATA TO INCLUDE HOVER AUTOPILOT MODES AND CAT A/B/PERFORMANCE CLASS TKOF AND LDG NOT AUTHORIZED EXC FOR ACFT USING APPROVED ALTERNATIVE METHODS OF COMPLIANCE DUE TO 5G C-BAND INTERFERENCE PLUS SEE AIRWORTHINESS DIRECTIVES 2021-23-12, 2021-23-13”

Dover AFB is home to the 436th and 512th Airlift Wings which fly C-5M Galaxy and C-17 Globemaster airlifters. I asked the 436th whether its aircraft are using approved alternative methods for precision approaches as required by the NOTAM above. An affirmative answer would imply that C-5/C-17 systems are indeed potentially affected by C-band 5G.

The 436th declined to answer, nor would it comment on the presence of C-band 5G nearby. A 436th spokesperson would only go as far as saying that, “Dover Air Force Base has not had any impacts to the base, airfield operations or instrumentation systems from 5G disruptions at this time.”

More general FAA NOTAMs on 5G interference apply to a variety of other Air Force bases/joint bases including Joint Base Langley-Eustis in Viginia, home to the F-22-equipped 1st Fighter Wing and Air Combat Command (ACC) headquarters. Offering the same questions noted above garnered only a referral to SAF PA from an ACC spokesperson.

ACC’s silence on the matter was matched by Air Force Air Mobility Command which provided no detail on the status of its airlifter/tanker fleet with respect to 5G interference by the time this piece posted. In a follow-up phone call to ACC, the command’s spokesperson indicated that Air Force major commands were simply not commenting on 5G.

The Secretary of the Air Force’s office maintains that it has not expressly instructed Air Force units/commands not to comment on questions regarding 5G interference. Nevertheless, the lack of detail from any of the USAF commands, units I reached out to suggests some mutually understood determination not to comment on the impact of 5G.

There is a further wrinkle gone unanswered as well. In 2020, DoD kicked off dual-use 5G testing at a variety of Navy, Marine and Air Force bases, evaluating 5G command and control, interoperability and standards, “smart warehousing” capability and radar spectrum sharing with 5G. The bases include Hill Air Force Base; Joint Base Lewis-McChord, Nellis Air Force Base, Joint Base Pearl Harbor-Hickam, and Tinker Air Force Base.

Whether this dual-use testing includes C-band 5G and whether it has been suspended over interference concerns is not something the Air Force claims to know. The service’s outlook seems to be that no news is good news. A SAF spokesperson reemphasized that the Air Force was reporting no issues with 5G as of this afternoon.

Let’s hope that continues and that the Pentagon looks back on 5G as a technology for which it did not make enough preparation, learning a lesson in the process. For now, the Air Force has little to say about it.