Answering Your Questions About AD 2023-10-02 And The Potential 5G Interference

July 2023

Recently there have been many questions regarding potential 5G interference with Aircraft Radio Altimeter (Rad Alt) Systems by our technicians and customers. The FAA released AD 2023-10-02, which explains this situation and how to proceed. Duncan Aviation’s Avionics Tech Rep team would like to clarify this AD and keep you up to date on the current situation.

• 5G (5^thGeneration) Devices and 5.0 GHz WIFI are not the same thing. We want to start by clearing up this misconception. 5G is a standard that is set by the FCC for a device to be considered a 5G device. 5.0 GHz is a frequency Band that WIFI networks operate at. Yes, most devices connect to 5.0 GHz (as well as 2.4 GHz) WIFI so that you can "surf" the internet. Your 5G (5^th Generation) devices, when not connected to WIFI, connect to cell towers for voice and data on a C-Band frequency that is 3.7 GHz to 3.98 GHz frequency range.
• So how does this apply to aircraft? According to AD 2023-10-02,"This AD was prompted by determination that radio altimeters cannot be relied upon to perform their intended function if they experience interference from wireless broadband operations in the 3.7–3.98 GHz frequency band (5G C-Band). The FAA is issuing this AD because radio altimeter anomalies that are undetected by the automation or pilot, particularly close to the ground (e.g., landing flare), could lead to loss of continued safe flight and landing. Additionally, radio altimeter anomalies could lead to increased flightcrew workload and flightcrew desensitization to warnings." 

The AD explains that there are two types of aircraft, “radio altimeter tolerant airplane” and “non-radio altimeter tolerant airplane.” The FAA defines the two as follows: 

(1)For purposes of this AD, a “radio altimeter tolerant airplane” is one for which the radio altimeter, as installed, demonstrates the tolerances specified in paragraphs (g)(1)(i) and (ii) of this AD, using a method approved by the FAA. No actions are required by this AD for radio altimeter tolerant airplanes.

(i) Tolerance to radio altimeter interference, for the fundamental emissions (3.7–3.98 GHz), at or above the power spectral density (PSD) curve threshold specified in figure 1 to paragraph (g)(1)(i) of this AD.

(2) For purposes of this AD, a “non-radio altimeter tolerant airplane” is one for which the radio altimeter, as installed, does not demonstrate the tolerances specified in paragraphs (g)(1)(i) and (ii) of this AD.

• Currently, Duncan Aviation does not service aircraft that fit into the “radio altimeter tolerant airplane” category. The aircraft and avionics manufacturers will eventually confirm this. Also, at this time, there is not a certified solution to add filters, replace current rad alts, or procedures to test for interference.

The AD goes on to say: "some radio altimeters may already demonstrate tolerance to 5G C-Band emissions without modification. Some may need to install filters between the radio altimeter and antenna to increase a radio altimeter's tolerance. For others, the radio altimeter will need to be replaced with an upgraded radio altimeter as established by a new radio altimeter TSO, which will follow the existing international technical consensus on the establishment of the minimum operational performance standards (MOPS). The FAA considers this AD an interim action because additional rulemaking may be necessary once a new radio altimeter TSO is developed, approved, and available."

Therefore, this AD applies to ALL aircraft types that we service at Duncan Aviation. Per the AD, "This AD applies to all transport and commuter category airplanes equipped with a radio (also known as radar) altimeter. These radio altimeters are installed on various transport and commuter category airplanes, including but not limited to, the airplanes for which the design approval holder is identified in paragraphs (c)(1) through (18) of this AD.

• What can we currently do at this time to assist our customers with this? At this time, all that we can do is educate our customers on the AD and keep them informed as new information comes out from the industry on this topic. As we already mentioned, there is not yet a certified solution to add filters, replace current rad alts, or procedures to test for interference. Per the AD, the flight crew will need to install a copy of the snapshot from the AD below into their AFMS. 

"i) AFM Revision After June 30, 2023

For non-radio altimeter tolerant airplanes, do the actions specified in paragraphs (i)(1) and (2) of this AD.

(1) On or before June 30, 2023, revise the Limitations Section of the existing AFM to include the information specified in figure 4 to paragraph (i) of this AD. This may be done by inserting a copy of figure 4 to paragraph (i) of this AD into the existing AFM. Incorporating the AFM revision required by this paragraph terminates the AFM revision required by paragraph (h) of this AD.

(2) Before further flight after incorporating the limitations specified in figure 4 to paragraph (i) of this AD, remove the AFM revision required by paragraph(h) of this AD.

Figure 4 to paragraph (i)— AFM Revision for Non-Radio Altimeter Tolerant Airplanes"

If you have any further questions, please feel free to contact the Duncan Aviation Avionics Tech Rep Group. You may also reference Duncan Aviation’s 5G-Be Prepared landing page at www.DuncanAviation.aero/5G.

Duncan Aviation Avionics Tech Rep Group