Date: 201911
Local time of day: 0601-1200
Location: LGA.Airport, NY
Flight conditions: VMC
Light: Daylight
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Climb
Airspace: Class B LGA
ATC / advisory: TRACON N90
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Clearance
Contributing factors: ATC Equipment / Nav Facility / Buildings; Procedure; Airport
Primary problem: Airport

Narrative: Prior to takeoff; we received an 'EFIS COMP MON' caution due to the magnetic anomalies near the runway that is addressed in our company bulletin. Since the caution message remained displayed as we entered the runway; we both (Captain and First Officer) set our AHRS (Attitude and Heading Reference System) to 'DG' (Directional Gyro) mode w/ the correct magnetic runway heading of '135 degrees' per recommended company procedure.After departure upon reaching 400 feet; the First Officer called for 'Heading' and we began a turn to 180 degrees per SID. As we're accelerating towards Vt-10; the First Officer calls for 'Flaps Up; After Takeoff Checklist' where the Captain proceeds to clean up the aircraft as well as change the AHRS back to 'MAG' (Magnetic) mode; considering we were now airborne; expected to be free of from any magnetic anomalies. As we are turning through a heading of 150 degrees in 'MAG' mode; the HSI (Horizontal Situation Indicator) on both PFD's (Primary Flight Display) jumps 30 degrees to the left almost simultaneously. Because of this; the new HSI indication now gives us false heading information by 30 degrees and as the First Officer rolls out on a 180 degree heading per departure SID; we are now in actuality; on a heading of 210 degrees which puts us right of course for the SID. At this time; ATC realizes the discontinuity and instructs us to make an immediate 'sharp' left turn to a heading of 020 degrees to correct the course. The First Officer took immediate correction to a 45 degree bank turn towards the newly assigned heading where while in the turn; the 'Bank Angle' aural sounded for 3 seconds. Once on correct heading of now 020 degrees; the 'EFIS COMP MON' caution reappears once again. At this time to prevent this issue from reoccurring a second time; we set both AHRS back to 'DG'; corrected our HSI with the standby compass and did not revert back to 'MAG' until we were above 10;000 feet. Once back in 'MAG'; the caution extinguished and the crew continued the flight with no further incident. Due to the severity of the magnetic anomalies in the LGA area; it would be highly recommended to have a suggested altitude that could be listed in our company bulletin's to let the pilots know a safe altitude for when to return the AHRS back to 'MAG' mode from 'DG.' That way this type of magnetic interruption doesn't affect future flight crews on this specific departure.




Synopsis: CRJ-200 Captain reported that a magnetic anomaly on departure resulted in an erroneous heading indication and a clearance deviation.