Regulatory Alert: FAA Proposes Deadlines for Retrofitting Airplane Altimeters to Ensure Safe Operations in 5G C-Band Environment

The Federal Aviation Administration (FAA) released a proposed rule on January 10 that would create mandatory deadlines for airlines to retrofit their radio altimeters to ensure their airplanes can safely conduct low-visibility operations in a 5G C-Band environment. A requirement for airlines to retrofit their airplanes would bring the industry one step closer to a long-term solution as the telecommunication companies continue to expand their 5G C-Band network across the country this year. However, the proposal raises questions as to whether the airlines can retrofit their altimeters within the timeframe proposed to avert potential operational disruptions.

In the proposed rule, FAA would set two separate deadlines in the form of an airworthiness directive. First, operators of any transport or commuter category airplanes would be prohibited from conducting low-visibility operations after June 30, 2023, unless the airplane is (a) equipped with a radio altimeter that meets certain standards and (b) operating at an airport identified by the agency through its FAA Domestic Notice system. Second, FAA would require that airplanes conducting air carrier operations under Part 121 be equipped with a radio altimeter that meets certain minimum performance standards by February 2024.

FAA is expected to publish the proposed rule in the Federal Register tomorrow, triggering a 30-day comment period - ending on Friday, February 10 - for industry stakeholders and the public to provide feedback. AAAE will be responding to the proposal, in coordination with our industry partners, emphasizing the need to set reasonable deadlines for compliance that recognize the supply chain and logistical challenges with retrofitting a U.S. fleet that is comprised of nearly 8,000 airplanes. 

Background. In December 2021, FAA found that radio altimeters could not work properly if they experience 5G C-Band signal interference and issued an airworthiness directive for all transport and commuter category airplanes. The directive prohibited airplanes equipped with these altimeters from conducting certain low-visibility operations at airports identified by FAA through NOTAMs. In January 2022, Verizon and AT&T voluntarily implemented temporary mitigation measures around airports located in the 5G C-Band network, which made it easier for airplane manufacturers to demonstrate to FAA that their altimeters were not susceptible to potential interference. This has allowed an overwhelming majority of the U.S. fleet to continue to conduct low-visibility operations at the affected airports.

Necessity of Retrofit Deadlines. In early 2022, FAA developed a temporary process for allowing a significant portion of the U.S. fleet to conduct low-visibility operations in a 5G C-Band environment. This process required manufacturers to request an approval, called an 'alternative method of compliance' (AMOC), for each make and model airplane. Each AMOC approval is specific to an individual airplane model and contains a list of runways and airports where the airplane is approved to conduct low-visibility operations. There are several factors that require a change in the process:

Expanding 5G C-Band Network: Verizon and AT&T continue to expand their 5G C-Band network into new markets each month. By the end of 2023, this network is expected to cover most of the contiguous United States. In addition, another 19 telecommunication companies are expected to gain access to the remaining 180 MHz of C-Band spectrum in late 2023, which will further expand the presence of 5G C-Band signals.

Removing Temporary Mitigation Measures: The voluntary mitigation measures and buffer zones that were implemented by Verizon and AT&T in January 2022 were only designed to be temporary in nature. Both companies are anxious to remove many of the mitigation measures and maximize the use of their 5G C-Band antennas and base stations. Some of the mitigation measures, however, are expected to remain in place.

Finding Permanent Solution: FAA's current approach involves the identification of affected airports through NOTAMs and issuing case-by-case AMOC approvals for specific makes and models of airplanes based on the location of 5G C-Band antennas near airports. FAA and industry have recognized the need for a permanent process, especially with the network expanding this year and moving into 2024, and this will bring the agency one step closer.

Summary of FAA's Proposed Rule. FAA's proposal, if adopted, would mark a significant shift in how the agency evaluates and approves low-visibility operations at airports where 5G C-Band signals are present. Highlights from our review of the proposed airworthiness directive are provided below.

Overall Approach: The proposed directive would prohibit any transport or commuter category airplane from conducting low-visibility operations after June 30, 2023, unless the airplane is (a) equipped with a radio altimeter that meets minimum performance standards and (b) operating at an airport identified by the agency through its FAA Domestic Notice system.

Types of Low-Visibility Operations Prohibited: Unless the airplane is equipped with an altimeter meeting certain performance standards, the proposed directive would prohibit the following types of operations after June 30: (1) ILS Instrument Approach Procedures (IAP) SA CAT I, SA CAT II, and CAT III; (2) automatic landing operations; (3) manual flight control guidance system operations to landing/head-up display (HUD) to touchdown operation; and (4) the use of enhanced flight vision system (EFVS) to touchdown under Part 91.

Airports Listed in FAA Domestic Notice System: An airport would be listed in the FAA Domestic Notice system if the telecommunications companies-including Verizon, AT&T, and any others that gain access to C-Band spectrum-have agreed to voluntarily limit their 5G deployment at the request of FAA. 'Domestic Notices' are special notices or notices containing graphics pertaining to almost every aspect of aviation. You can find more details here. In the proposal, FAA did not provide any details on how many airports would be included in the Domestic Notice system.

Mandatory Retrofits: FAA would require that airplanes conducting air carrier operations under Part 121 be equipped with a radio altimeter that meets certain minimum performance standards by February 1, 2024.

Key Takeaways from FAA's Proposed Rule. In the proposal, FAA provided many details regarding its efforts to address safety issues caused by deployment of the 5G C-Band network. Based on our initial review, here are some key takeaways and our analysis of FAA's proposed airworthiness directive and what it could mean moving forward:

Codifying Ongoing Voluntary Retrofit Efforts: Beginning May 2022, FAA, Verizon, AT&T, and the aviation industry, including AAAE, engaged in a series of meetings to develop a plan and timeline to retrofit the entire U.S. fleet. The final plan was phased over time through July 2023 and based on the aircraft and altimeter type. However, the plan was ambitious, and airlines have already expressed significant concerns over the ability to complete the voluntary retrofits under the timeline set by FAA. The proposal released yesterday is part of the agency's efforts to codify a voluntary initiative that has been ongoing since last year. 
 
Ability of Airlines to Meet Proposed Deadlines: FAA provided that the proposed deadlines-July 2023 and February 2024-were deemed 'reasonably practical' to retrofit altimeters and 'consistent with FAA policy.' In November 2022, airlines directed a letter to the Biden Administration, emphasizing that they were not on schedule to retrofit their aircraft's altimeters by mid-2023 because of supply chain challenges and equipment availability. The proposed rule raises significant questions as to whether the airlines will be able to meet the deadlines proposed by the agency and, thus, avert potential disruptions.

Cost of Retrofitting Altimeters: FAA estimated that the cost of complying with the proposed rule for the industry is about $26 million. This assumes about 180 airplanes would require replacement of the radio altimeter and 820 airplanes would require the addition of 'filters' to comply with the proposed modification requirement. However, we believe this is a significant underestimate of the overall retrofit costs because FAA stated that its estimate does not include the airlines' voluntary retrofits and upgrades for over 7,000 airplanes that have been occurring since summer 2022.

Continued Reliance on Voluntary Mitigation Measures: One concerning part of FAA's proposal is that the minimum performance standards for altimeters were developed based on the assumption that Verizon and AT&T maintain at least some mitigation measures around airports for the foreseeable future. The standards further assume that 19 additional telecommunication companies implement these same mitigation measures when they gain access to their portion of the C-Band spectrum later this year. If any of these companies choose not to maintain or implement these measures, then this would reduce the number of airports where airlines may be permitted to operate and may require further altimeter upgrades.

Elimination of 5G NOTAMs and AMOCs: FAA is currently issuing 5G NOTAMs that identify the airports where certain low-visibility operations are prohibited because of the presence of potential 5G C-Band signal interference. In addition, the agency has issued a wide range of AMOCs for individual aircraft that permit these operations at specific airports across the country. Under the proposal, FAA has proposed minimum performance standards for altimeters that eliminate the need for FAA to issue NOTAMs and AMOC approvals. If an altimeter meets the standards, then the airplane would be permitted to operate at any airports listed in the Domestic Notice system.

What's Next? After FAA publishes the proposed rule in the Federal Register, industry stakeholders and the public will have 30 days to submit comments to the agency. The deadline is expected to be Friday, February 10. AAAE will be working with our members and industry partners to respond to the proposal. Our goal is to ensure that operational disruptions are minimized and the federal government develops and implements long-term, permanent solutions that allow aviation and the 5G C-Band network to safely co-exist.