Date: 202202
Local time of day: 1801-2400
Location: ZZZ.Tower, US
Flight conditions: VMC
Light: Night
Aircraft: Medium Large Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: INS / IRS / IRU
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Commercial
Human factors: Troubleshooting; Workload; Confusion; Distraction; Human-Machine Interface
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Unstabilized Approach
Detector: Automation Aircraft Terrain Warning; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft; Airspace Structure; Software and Automation; Procedure; Equipment / Tooling
Primary problem: Aircraft

Narrative: During the flight from ZZZ1 to ZZZ; we received Ground Proximity Warning System (EGPWS) Terrain; Terrain; Pull Up; annunciator on the right downwind about to turn to base for the visual to Runway XXL at ZZZ right after ATC approved us for the visual. This flight was at night with clear sky and runway insight. We received the Terrain; Terrain; Pull Up alert approximately abeam midpoint between IF (Initial Fix) and FAF (Final Approach Fix) at above 2000 ft within about 3NM on the right downwind. The pilot flying (FO) immediately responded to the alert by clicking the Autopilot off and followed the appropriate recovery procedure. As soon as the pilot flying initiated the recovery procedure the alert was eliminated. Both pilot flying (FO) and pilot monitoring (CA) looked outside and we had no visual of any terrain. As a result of this alert; we were unstable for the approach and we made a decision to terminate the approach and get radar vectors for another attempt for the RNAV (GPS) Runway XXL. ATC; began to give us radar vectors to the right downwind with a descent to 3000 ft. At 3000 ft on the right downwind we received another brief Terrain; Terrain; Pull Up; annunciator. The pilot flying immediately initiated the recovery procedure and the alert was immediately eliminated. Pilot monitoring asked ATC if there is any known terrain at our current position and altitude or if anyone has reported [a] similar alert. ATC informed us there was no terrain and no reports. The pilot monitoring noticed IRS REVERTED white message on the PFD during the Terrain; Terrain; Pull Up; annunciator and repositioned the aircraft coordinates not certain if this would have caused the Terrain; Terrain; Pull Up alert. We continued the approach and landed safely with no further issues. ATC stated they will disseminate the information to identify if there is any known issue. Possibly address the IRS issue if it was related to the false alert. Also; it might be related to the 5G interference and need further look into.




Synopsis: An air carrier Captain reported receiving Terrain Alerts on downwind on two approaches even though they were at altitudes above terrain and as assigned from ATC.  The alerts caused an unstable approach requiring a go around.