Date: 202201
Location: ORD.Airport, IL
Flight conditions: IMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B ORD
ATC / advisory: TRACON C90
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance; Flight Crew Overcame Equipment Problem
Contributing factors: Environment - Non Weather Related; Aircraft
Primary problem: Environment - Non Weather Related

Narrative: The incident occurred today on leg 3 of day 5 for me on reserve. I was the Pilot Flying. We were cleared to 4;000 ft. to join from the north on a 240 heading intercept for the RNAV GPS 27R approach into ORD. We had made the turn to 240 in IMC to intercept and I armed LNAV. The aircraft started to bank in the opposite direction (left) of desired course. We were queried by ATC to make sure we were aligning with 27R. I corrected our course with no incident but have never seen the aircraft pitch in that way when already intercepting to the right. We were told to call TRACON that 3 other aircraft earlier that day had experienced something similar with a bank to the left.


Second narrative: We were cleared for a 30 degree intercept to RNAV Runway 27R ORD outside WELEV at 5;000. It was smooth and clear. A perfect intercept. We were established on something like a 240 head in to a 273 inbound intercept. As we approached where the aircraft would normally start leading the intercept turn; as the curved line showed; the aircraft started a turn to the LEFT; instead of the right; towards the airport. The aircraft only turned a couple degrees opposite the desired course as we approached and flew slightly through the course as the aircraft corrected and turned back to and intercepted the inbound course. I think we would have either selected heading and corrected it or turned off the autopilot sooner if we were in IFR. The fact that we were VFR seemed to give us just a few seconds to try to understand and see with the aircraft was trying to do. ATC ask if we were lined up for 27R and noted that they had had several prior issues with the RNAV approach that day. We confirmed we were correcting on course and continued the approach without incident. The incident occurred very close to the City of Chicago leaving us wondering if 5G interference might have played a roll? I all my years of flying; I have never seen an aircraft turn opposite to the inbound course in this situation. I realize there is an issue with LNAV in this aircraft on an intercept course if you are not wings level when it is selected. In this situation; we were wings level; established and on a very easy intercept angle for the inbound.


Synopsis: Flight crew reported their aircraft turned the wrong direction when intercepting final. ATC advised the reporters that three other aircraft did the same thing leading the pilots to think it might be 5G interference.