EMB ERJ 145 ER/LR
Flight Crew Air Transport Pilot (ATP)
Human-Machine Interface
Aircraft Equipment Problem Less Severe
Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Aircraft; Human Factors
During descent into RDU; on the ALDAN1 RNAV arrival; we were given the 'landing southwest' transition. The FMS was programmed for the ILS to Runway 23R. The FMS was reviewed and the waypoints were correct with no multiple waypoints. Upon crossing the ALDAN fix; the Flight Guidance went from LNAV to ROLL mode. We immediately put the FGC into HDG mode and turned to the next fix. ATC was notified and we were subsequently given direct to a fix on the ILS approach. The FMS seemed to sequence to the next fix correctly; but the FGC did not. This particular aircraft's FMS was software version 4.8.
Descending into RDU on the new RNAV ALDAN1 arrival; the FMS had a glitch and kicked off the lateral mode of the autopilot and sent the plane into Roll mode when it should have started a turn. We reacted immediately and put the plane on course then re-selected the next fix. The FMS appeared to sequence okay; but the FGC jumped into Roll mode. There were no issues with deviating off course because of our reaction; but did advice ATC; from that point they gave us direct to a fix on the arrival. It was a clear day.
EMB145 flight crew reports an FMC anomaly crossing ALDAN on the ALDAN 1 arrival to RDU. Although the FMC was programmed for the Runway 23 transition the Flight Guidance went into roll mode at ALDAN and was quickly corrected.