Flight Crew Air Transport Pilot (ATP)
Human-Machine Interface; Situational Awareness; Workload; Confusion
Aircraft Equipment Problem Critical; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew FLC Overrode Automation; Flight Crew Returned To Clearance
Aircraft
In cruise flight well outside ROA we were inbound on the SBV4 arrival in RDU. ATC then issued us a vector off course about 10-15 degrees to the left. A few minutes later we were re-cleared direct to ROA via the ALDAN 1 Arrival. I loaded the arrival into the FMS and selected the ROA transition. Prior to executing the change; I verified with the First Officer and noted that ROA was in the TO line of the FMS. However for some reason the FMS did not give us a direct course but instead place the course to the right of the aircraft. In order to intercept the autopilot attempted to take a hard intercept to the right to get on course. I saw what was happening and reselected direct ROA in the FMS to correct the problem. However due to the heading change ATC did query us if we were proceeding direct ROA. ATC made no further issue or remarks and we proceeded to RDU uneventfully. Reliance to automation. Uncommanded response to input in the FMS. I would be more vigilant in ensuring the FMS is showing a direct to line to the selected fix.
A CRJ-200 FMS did not proceed direct ROA after ATC vectored the aircraft off the ALDAN 1 Arrival then recleared direct ROA for the transition.