Flight Crew Air Transport Pilot (ATP)
Distraction; Situational Awareness
Aircraft Equipment Problem Less Severe; Airspace Violation All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Overcame Equipment Problem
Aircraft; Human Factors
Departing [on] RNAV Departure. At the positive rate callout I called for gear up; speed; and nav. I was following the Flight Director through 300-500 when I realized the NAV mode hadn't captured and we were still in heading mode. I disregarded the Flight Director and turned to the left back to our course. The Captain had tried three times throughout the departure to arm the NAV mode to no avail. By the time I noticed the deviation and turned on course we were approximately one dot to the right of our course. I believe we might have penetrated a Prohibited area. On the fourth attempt the lateral mode armed and I flew the remainder of the departure without incident. After several minutes we were given a phone number to call. [On arrival] I was being vectored to final for RWY XY. I switched to green needles and armed the NAV mode to intercept the LOC with autopilot engaged. The autopilot captured the LOC and almost immediately dropped the Lateral NAV mode and reverted to ROL mode. The Captain tried several times to rearm the Approach mode to no avail. I disconnected the autopilot and followed the PAPI to an uneventful landing using raw data.
EMB-145 First Officer reported that a malfunctioning Lateral Navigation mode caused a course deviation on departure and reversion to a raw data; hand-flown approach.