Radar Altimeters And 5G Cellular Interference

The FAA wants to know whether and how the new cellular standard affects installed equipment.


If you listened much to the cellular telephone companies talk about the ongoing rollout of 5G performance standards for your devices, you might think it was the best thing since sliced bread, canned beer and kissing on the first date. The FAA isn’t so sure, however, and in early November published a Special Airworthiness Information Bulletin (SAIB AIR-21-18), Risk of Potential Adverse Effects on Radio Altimeters, seeking additional information from manufacturers and operators.

The SAIB results from an RTCA report entitled, “Assessment of C-Band Mobile Telecommunications Interference Impact on Low Range Radar Altimeter Operations.” Among other things, the RTCA found “a major risk that 5G telecommunications systems in the 3.7–3.98 GHz band will cause harmful interference to radar altimeters on all types of civil aircraft—including commercial transport airplanes; business, regional, and general aviation airplanes; and both transport and general aviation helicopters.”

The RTCA report results from testing of representative radar altimeters to determine their tolerance to expected 5G signals. The test results “clearly indicate that this risk is widespread and has the potential for broad impacts to aviation operations in the United States, including the possibility of catastrophic failures leading to multiple fatalities, in the absence of appropriate mitigations,” according to RTCA.

Part of the problem is that the existing Technical Standard Order (TSO) under which radar altimeters are approved—TSO-C87a—“does not provide criteria for compatibility with adjacent band operations, including potential impacts associated with wireless communications system deployments,” according to the FAA’s SAIB.

In turn, the FAA “recommends that radio altimeter manufacturers, aircraft manufacturers, and operators voluntarily provide to federal authorities specific information related to altimeter design and functionality, specifics on deployment and usage of radio altimeters in aircraft, and that they test and assess their equipment in conjunction with federal authorities. Results from that testing and assessment should be reported to the appropriate civil aviation authorities (CAAs) and spectrum regulators.”

The SAIB includes specific recommendations for operators, avionics manufacturers and aircraft makers. For example, radar altimeter makers are requested to “submit receiver RF selectivity, interference tolerance masks, and baseline operational specifications for each model number in production or still in use, and approximate numbers of each radio altimeter model currently in service in the United States,” in addition to analyzing and testing specific radalt models.

Airframe manufacturers also are urged to conduct testing and analysis on “loss of function, and erroneous or misleading radio altimeter data from potential harmful interference” in the radio spectrum adjacent to that used by radar altimeters, and determine “any operational restrictions necessary or actions to take to maintain safe operations with radio altimeter equipment susceptible to harmful interference due to wireless broadband operation.”

“Operators should ensure their pilots are aware of the potential degradation of the radio altimeter capabilities and any means to compensate for in-flight radio altimeter anomalies,” the SAIB encourages. “Operators should ensure their pilots are aware of the potential degradation to the capabilities of safety systems and other equipment dependent upon radio altimeters and any means to compensate for resulting anomalies. Consider both the loss of function of the safety systems and other dependent systems and the manners in which they may malfunction.”

Operators also are requested to remind passengers that all portable electronic devices “in checked baggage (including smartphones and other devices) should be turned off and protected from accidental activation.” They also should remind passengers that “all portable electronic devices in the cabin” be set to a non-transmitting mode or turned off.


In mid-November, the NTSB brought some good news to the aviation safety front when it announced U.S. civil aviation accident rates for 2020 resulted in decreases in fatalities overall. The reduction in lives lost came as 2020 flight activity was down across different all operational categories, to no one’s great surprise.

According to the NTSB, most fatalities in 2020 occurred as a result of general aviation operations. In 2020, there were 332 fatalities, compared to 414 the year before. Coupled with the overall reduction in activity, general aviation’s 2020 fatal accident rate was 1.049 accidents per 100,000 flight hours, which compares favorably to 2019’s rate of 1.064.

Meanwhile, accidents involving FAR Part 135 on-demand operations—charters, air taxis, air tours and medical services when a patient is on board—claimed 21 lives in 2020, which also is a reduction from 2019, when 32 people died in such operations. After two consecutive years with airline passenger fatalities, there were no fatal accidents involving Part 121 air carriers in 2020, according to the NTSB.

There’s a caveat: The NTSB’s 2020 statistics include investigations that are still ongoing, so “they do not detail potential reasons for the accidents and fatalities in U.S. aviation,” the Board said. The table reproduced on page 27 presents the raw NTSB numbers for 2020. An annual summary of U.S. civil aviation accidents, updated through 2019 and including historical comparisons, was scheduled for release in December.


Please enter your comment!
Please enter your name here