Date: 202202
Local time of day: 1801-2400
Location: BOS.Tower, MA
Flight conditions: IMC
Aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B BOS
ATC / advisory: Tower BOS
Aircraft component: Radio Altimeter
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft; Environment - Non Weather Related; Weather
Primary problem: Ambiguous

Narrative: Cat3 Autoland thoroughly briefed and flown based on ATIS 1/4 mi and VV (Vertical Visibility) 200 ft. On approach; prior to feathered notch; ATC reported RVR as 3000 ft. TD (Touchdown) and 2400 ft. RO (Rollout) with significant tailwind until ~ 200 ft. and changing to small headwind below that altitude. Also; ATC advised that previous aircraft reported breaking out/ at 100-200 ft. Since weather was marginal; I elected to continue with the autoland approach. We extended landing gear and flaps earlier than normal; but tailwind still made it difficult to slow the aircraft. Aircraft was approximately 20 knots fast at 1000 ft. and acknowledged and correcting at that stability gate and callout. We were stable at +12-15 kts. at the 500 ft. gate; and with Cat 3 Dual displayed; the callout was made. LAND was annunciated by 350 ft. and FO (First Officer) called 'Approaching Minimums' at 200 ft. RA (Radio Altimeter). At this point; I could begin to see Runway 04R lighting and portions of runway thru bottoms of ceiling. FO called 'Minimums' at 100 ft. RA and after verifying Cat 3 Dual displayed; I responded with 'Landing'. Then things got interesting. Nearly simultaneous with my 'Landing' call; I noticed the red autoland light illuminated for no obvious reason. The autopilots were still engaged and there were no master cautions or warnings. The aircraft was clearly aligned with Runway 04R touchdown zone and we were below the ceiling and; as advertised; had 3000 ft. RVR. I opted to disconnect the autopilot and auto thrust between 80-100 ft. and continued to land with more than adequate visual reference as the safest option. I did not notify the Tower Controller of failed autoland for two reasons. First; the Tower was busy coordinating a go-around with a following flight and then we needed to concentrate on and clarify taxi instructions as Boston controllers were using Runway 4L/22R as an active taxiway. Secondly; at the time of the event; I did not suspect 5G interference so it was not reported to Tower or Dispatch; but we did document failed autoland in a maintenance write up. Post flight review of the red autoland illumination causes; and a process of elimination during later crew debrief; lead me to suspect 5G interference caused a 15 ft. (or more) discrepancy between radar altimeters resulting in the malfunction. The autopilots did not disengage nor did we notice any LOC/GS scales or flight director bars flashing for excessive deviation or signal loss.




Synopsis: Air carrier Captain reported autoflight anomalies on approach to BOS; citing 5G interference with the radio altimeter as the possible cause.