Radio Altimeter 5G Interference

Effectivity: All Learjet Aircraft Equipped with Radio Altimeters

ATA 34

By: Kevin Ensminger – Learjet Service Engineering

In response to FAA AD-2021-01169-T regarding 5G C-Band interference with aircraft on-board radio altimeter systems, Collins and Honeywell released Service Information Letters (SIL) describing the actions they have or are taking to mitigate this issue.

Collins SIL number ALT-55B-21-1 for the ALT-55B Radio Altimeter system provides a synopsis of the manufacturers recommendations regarding the 5G effects on Collins ALT-55B radio altimeters ability to mitigate 5G interference. The ALT-55B Radio Altimeter was an optional installation on the Learjet 35A/36A, standard on Learjet 55/B/C, standard on Learjet 60-002 – 60-278, and optional on Learjet 60-279 – 60-300.

Collins SIL number ALT-4000-21-1 for the ALT-1000 and ALT-4000 Radio Altimeter system provides a synopsis of the manufacturers recommendations regarding 5G effects on Collins ALT-1000 and ALT-4000 radio altimeters ability to mitigate 5G interference. The ALT-4000 Radio Altimeter was an optional installation on Learjet 60-279 – 60-300, standard on Learjet 60-301 – 60-430, optional on the Learjet 40/45, and standard on all Learjet 70/75 aircraft.

Honeywell SIL number D202201002193 for the KRA-405B Radio Altimeter system describe the limited 5G interference resistance of this radio altimeter and Honeywell’s efforts to improve this resistance. The KRA-405B was standard on 31A-167 – 31A-242.

Honeywell SIL number D202201002191 for the RT-300 Radio Altimeter system informs the reader that this radio altimeter system is currently not 5G interference resistant as defined by the AD. The SIL describes Honeywell’s efforts to improve the 5G interference resistance performance. The RT-300 was the dominant radio altimeter system installed on the Learjet 40/45.

Please reference the manufacturers’ Service Information Letters for more details regarding 5G interference to determine if and how this equipment may affect your aircrafts’ operation. The FAA and Radio Technical Commission for Aeronautics (RTCA) are continuing evaluation to determine the effects on aircraft radio altimeter performance.