Citation X (C750)
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 150; Flight Crew Total 3075; Flight Crew Type 600
Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types
Flight Crew Diverted; Flight Crew Landed As Precaution
Aircraft
Daytime VMC flight. Power up; APU start; cockpit setup etc was all normal. Then the APU shut down after 25 mins of running with a FAIL message. We ran the checklist; called Maintenance; were advised to use a GPU in an effort to get the APU restarted; which we did. About 30 minutes later with our passenger waiting we were able to get the APU back up; engines started; flight plan re-loaded; systems checked; and proceeded to taxi. Normal taxi and takeoff; but either during the takeoff roll; rotation; or second segment climb we experienced a lateral navigational anomaly where our heading indicator values seemed to have flipped 180 degrees on both sides. Attitude indicators still worked fine. It is worth noting this is an AHRS (Attitude and Heading Reference System)-equipped Citation X; not IRSs (Inertial Reference System); to provide attitude and heading. Both the course displayed on the MFDs (Multi-function Flight Displays) and HIs (Heading Indicators) were giving the same misinformation. To simplify; east was west and north was south. In Nav mode the FD (Flight Director) was commanding turns in the opposite direction of what was called for. I immediately requested a vector once we realized what was happening. Luckily we were in VMC so it was a fairly straight-forward procedure from there. We used the mag compass; primary attitude indicators and altimeters on our PFDs [Primary Flight Display] to fly and try to work the issue; then asked to divert to [a nearby alternate] in an effort to help maintenance and passenger. We received no EICAS (Engine-Indicating and Crew Alerting System) messages nor indications on the PFD that there were any data mis-compares; avionics failures; or revisionary modes enabled. We were vectored onto final; visual approach and landing were normal.
[Report narrative contained no additional information.]
CE750 flight crew reported a navigation anomaly shortly after takeoff; and diverted to a nearby alternate.