Regional Jet 700 ER/LR (CRJ700)
Flight Crew Air Transport Pilot (ATP)
Confusion
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Aircraft Equipment Problem Dissipated; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Aircraft; Environment - Non Weather Related
While climbing on the DARTZ 1 RNAV DEPARTURE after crossing OWLLS; I noticed the autopilot initiated a late turn and as a result we were of course to the north. The Captain noticed that both of our DG's [Directional Gyros] had turned nearly 90 degrees from where they should be. Within seconds; ATC advised us that we were off course and asked us to fly a heading. We advised him that we were having navigation issues and we were flying by the standby compass. I switched the autopilot from NAV Mode to Heading Mode to fly the assigned heading by the compass. I flew the plane and handled the radios; while the Captain consulted the QRH. Just as the Captain was troubleshooting the AHRS Comp Mon issue the autopilot initiated a turn to the right. Immediately; we took it out of heading mode and let the airplane fly in Roll Mode to continue on the assigned heading. After complying with the EFIS COMP Mon QRH procedure; we were able to establish a normal operating system where both DG's matched the standby compass. We advised ATC that our navigation system was operational. We accepted a clearance direct to an enroute fix. We asked ATC to advise us of any course or heading abnormalities which they may notice while enroute. When ATC handed us off to the next facility; they advised us that no abnormalities were observed. Upon landing; the Captain entered the discrepancy into the maintenance log. Failure of the AHRS system to provide accurate information despite execution of the SOP.
We were complying with the SOP instructions for EFIS COMP MON message mitigation on takeoff from an airport with known extreme magnetic deviation anomalies. After wings level southbound on the departure; we re-selected mag mode with both DG [Directional Gyro] systems. At this point; both compass systems slewed significantly in the same direction and there was a dramatic map shift. With incorrect information displayed; we were trying to figure out what was going on laterally. ATC advised us it looked like we were off the RNAV course. I advised him we were having a navigational issue. He gave us a heading to fly; followed by two more turns to headings to fly. We attempted to fly the headings and diagnose our problem. It took us a minute or so to realize after the heading stabilized that the primary problem was that the headings presented were inaccurate. About this time; the headings; which had initially slewed incorrectly together began to diverge and we received red MAG flags with other sundried AHRS messages. We reverted to the compass. We advised ATC that we were having heading problems and that we would revert to compass headings only; until we could fix the problem. He got us established southbound and handed us off to the next controller. After complying with the QRH for EFIS COMP MON; we were eventually able to re-establish normal system operation and continue to our destination. At the destination; we contacted maintenance control and entered the discrepancy in the logbook. Local maintenance is working on the aircraft.The failure of the AHRS system to maintain heading information after being returned to mag mode following the departure from the airport with known extreme magnetic anomalies; despite adherence to the SOP Appendix A procedure.
CRJ-700 flight crew experiences AHRS heading anomalies departing DFW resulting in a track deviation on an RNAV departure. ATC issues headings and the system is returned to normal operation a few minutes later.