U.S. Airlines Warn 5G Safety Risks Go Beyond Altimeters

Delta Air Lines 737-88
Credit: Nigel Howarth/AWST

Interference with key aircraft systems that rely on radio altimeter data and a lack of approvals at high-traffic airports may force airlines to avoid operations in many 5G C-band wireless service areas debuting Jan. 19, despite FAA sign-offs that cover equipment in a majority of mainline fleets.

The FAA in recent days has approved two Collins Aerospace radio altimeters, the LRA-900 and LRA-2100, as being safe to operate on approaches to hundreds of runways adjacent to 5G-C band transmitters. The at-risk runways were flagged in a series of notices to air missions (Notams) that detailed more than 1,000 airport-specific operational limitations issued beginning Jan. 13.

The alternative means of compliance (AMOC) approvals, granted to Boeing and Airbus, cover 737s, 747s, 757s, 767s, 777s, MD-10s, MD-11s, A320s, and A350s equipped with either of the Collins units. But the AMOC are limited, applying only to low-visibility operations such as Category II and III approaches, Required Navigation Performance procedures with Authorization Required, and related “automatic landing operations,” as detailed in a December airworthiness directive that established the limitations. 

The approvals do not cover all onboard systems that use radar altimeter data, which details an aircraft’s precise distance above the ground. 

Airbus, Boeing and other stakeholders are working to determine aircraft model-specific ramifications and—if necessary—issue additional restrictions. With less than two days left before AT&T and Verizon Wireless begin the already twice-delayed initial rollout, many questions remain unanswered.

A Boeing multi-operators message issued to 737 fleet stakeholders Jan. 16 reflected the level of uncertainty aviation is facing.

"When operations are planned at a U.S. airport where the FAA has issued a NOTAM for 5G interference, the flight crew will need to be alert for system anomalies that may occur due to 5G interference,” Boeing wrote. "There may be some flight deck effects, and depending on the behavior of the radio altimeter system, there may be some impacts to autopilot [and] autothrottle behaviors.”

An FAA safety alert issued in December 2020 provided a partial list of functions that rely on radio altimeter data in some aircraft. They include traffic alert and collision avoidance systems, enhanced ground proximity warning systems, windshear detection, and stall-warning.

Some of the affected aircraft may be subject to airworthiness directives. The 787 fleet, which is not on the Boeing AMOC issued Jan. 15 and can therefore use restricted airports only in good weather, may experience 5G C-Band-related interference with engine and braking systems during approaches. Operators must account for the possibility when landing at any airport covered in a Notam, a directive slated for publication Jan. 18 said.

While MOMs are not mandatory, operator compliance with limitations they contain is a foregone conclusion for legal reasons, regardless of whether regulators take additional action. With the Jan. 19 deadline looming, manufacturers elect to take conservative approaches and issue restrictions while they are validating specific  concerns. This, the A4A letter suggests, could lead to significant operational disruptions. 

Another issue with the AMOC approvals is the lack of applicability at some busy airports. The list of hundreds of runways covered by each AMOC includes less than 20% of the busiest 100 airports ranked by both passenger and cargo traffic, an Airlines for America (A4A) analysis seen by Aviation Week concluded. Several of the 50 large airports flagged by the FAA as needing temporary buffer zones are among those not covered, including California’s Los Angeles International, New Jersey’s Newark Liberty International and Houston Intercontinental in Texas.

Airlines’ concerns prompted A4A to ask Verizon and AT&T to hold off its 5G C-band deployment within 2 mi. of runways flagged by the FAA as at risk of interference.

"Immediate intervention is needed to avoid significant operational disruption to air passengers, shippers, supply chain and delivery of needed medical supplies,” the association said in a Jan. 17 letter to the FAA, Transportation Dept., the White House and the head of the Federal Communications Commission.

"Because radio altimeters provide critical information to other safety and navigation systems in modern airplanes, multiple modern safety systems on aircraft will be deemed unusable causing a much larger problem than what we knew on January 5, 2022,” when the most recent deployment delay was announced, A4A added. "Airplane manufacturers have informed us that there are huge swaths of the operating fleet that may need to be indefinitely grounded.”

Reuters first reported the letter’s content.

The FAA said Jan. 16 that the two AMOCs cover about 45% of the U.S. commercial fleet and runways at “as many as 48 of the 88 airports most affected by 5G C-band interference.” 

The initial C-band deployment covers areas in 32 states. Several regions with major airports, including Atlanta and Denver, are not part of the initial rollout.

Aviation and wireless industry stakeholders have been sparring over the 5G C-band rollout ramifications for months. The wireless side points to successful deployments in other countries as evidence that U.S. aviation concerns, spearheaded by the FAA, are overblown. The FAA counters that an absence of evidence of any safety risk is not sufficient, and only testing and validation of how the new services, which use C-band frequencies close to ones long used in aviation, will satisfy the FAA. 

Retrofits are a likely long-term solution, but do not alleviate immediate concerns.

Sean Broderick

Senior Air Transport & Safety Editor Sean Broderick covers aviation safety, MRO, and the airline business from Aviation Week Network's Washington, D.C. office.


Who the heck from the FAA signed off on this when the decision was made?
5G is 5G utilizes OFDM (orthogonal frequency-division multiplexing), a waveform modulation technique also used by both LTE and IEEE 802.11 (Wi-Fi) (Telit website) and a WIKI page on radar altimeters said As of 2010, all commercial radar altimeters use linear frequency modulation - continuous wave (LFM-CW or FM-CW). I thought the different modulation methods would keep them from interfering (like FM and AM commercial radio stations.
From what I've read, the FAA were not involved. Simply put, the FCC saw a chance to make a lot of money and took it.
Air transport safety was not a consideration!
I think that most semi-aware folks have known for years that 5G was coming. This last minute kerfuffle over the problem is a product of the "kick the can down the road" philosophy, which seems to be practiced equally by both governmental and private bureaucracies. There's no reason for this to be such a developing "cluster festival" at this point in time.