Date: 202201
Local time of day: 1201-1800
Location: C90.TRACON, IL
Flight conditions: VMC
Light: Daylight
Aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Operator: Fractional
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class C MDW
ATC / advisory: TRACON C90
Aircraft component: Radio Altimeter
Component problem: Malfunctioning
Reporter organization: Fractional
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Troubleshooting; Time Pressure; Situational Awareness; Distraction
Second reporter function: Captain; Check Pilot; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft; Environment - Non Weather Related; Airspace Structure
Primary problem: Ambiguous

Narrative: We were on right downwind for RWY22R at 1900 MSL on the first of two almost identical flights. As we approached the base turn; I noted an amber R ALT flag in the PFD and the EICAS indicated a cyan 'FGC - A/T Rad Alt Invalid' CAS message. Our GPS track indicates the event occurred approximately above Laramie & 31st St. None of the three of us knew exactly the corrective action from memory; but it was apparent that the autothrottles were affected by a radar altimeter issue. The tower frequency was busy; working us between numerous arrivals and departures. We were coordinating inside the cockpit since I could not see the airport from my position on the left side of the aircraft. Between the long traffic pattern checklist; increased coordination in the cockpit; lots of radio traffic; configuring the airplane; discussing the implications of the CAS message; and tracking numerous targets outside; we were quite busy so we didn't have the opportunity to compare radar altimeter indications. We had briefed the possibility of radar altitude issues stemming from the rollout of 5G services; and we elected to disconnect the autothrottles and continue the approach to a normal landing.While we were aware of the possibility of radar altimetry issues due to the NOTAM at MDW and all of the industry publications as of late; we didn't really expect to have any issues with our operation. With a combined years of [aircraft type] operation between the three of us; we have found the radar altimeters to be supremely reliable; and none of us had seen that CAS message ever displayed prior to this occurrence. We discussed the 5G NOTAM during our preflight brief; but we had assumed (incorrectly) that it would only affect the listed operations. It was certainly a very unwelcome distraction during an especially high workload critical phase of flight.


Second narrative: [Report narrative contained no additional information.]


Synopsis: Pilots on a training flight reported a malfunction of the radio altimeters and autothrottles while on approach to MDW. The crew suspected the anomaly was 5G related.