Date: 201705
Local time of day: 1801-2400
Location: BOS.Airport, MA
Flight conditions: IMC
Light: Dusk
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B BOS
ATC / advisory: Tower BOS
Aircraft component: Navigational Equipment and Processing
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft; Weather
Primary problem: Aircraft

Narrative: Aircraft had been written up the day prior in the maintenance log for intermittent course guidance on approach. Aircraft was later tested and signed off and returned to service. Prior crew did not indicate any problems. On approach into BOS on the ILS to runway 27; at approximately 2800 ft MSL the localizer and glideslope on both PFDs displayed red X's. After two seconds the course guidance returned. Then went out again; then returned; and again - displayed a red X; then returned to normal operation.  During this phase of the approach; we were passing through several layers of IMC with each appearing as though it would be the last. At 1600 ft; 200 ft below the final approach fix altitude we broke out and were maintaining visual guidance to the runway when tower called simultaneously to call us off the approach and to re-sequence us back onto the approach at 2000 - and back into IMC. I immediately informed ATC we had navigation problems and red X's and were unable and that we must continue the approach visually. Tower was concerned about spacing for an aircraft which myself and the First Officer called in sight and had plenty of separation. Originally we were requested to maintain 170 kts to RIPPY FAF and were on that speed but we were able to slow to our final approach speed and the aircraft crossed runway 27 on runway 33L with our aircraft still on about 3 mile final. At the time of the incident; I immediately notified the tower that I was having navigation problems at about the same time as they asked us to go around. At that time; and to the best of my knowledge; our navigation problem was on both sides of the cockpit and related to our systems displays and not both navigational radios and antennas at the same time; therefore leading me to believe that I could also not trust the RNAV approach system I had on board as well. In the interest of safety; I made the decision not to re-enter IMC without knowing some form of reliable approach system on the aircraft was working. I had two alternates as well; both with weather far less than VFR requiring navigation systems and instrument approach procedures. I informed the tower we must land and we did so without incident. Factors leading to my decision were forecast weather being less than VFR at airports within fuel range of our aircraft; with weather at my two alternates being 800 and 1200 OVC.




Synopsis: EMB-145 Captain reported navigation issues but continued the approach in visual conditions after Tower instructed a go-around because the traffic was in sight and a reluctance to re-enter IMC.