Light Transport; Low Wing; 2 Turboprop Eng
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 200; Flight Crew Total 15750; Flight Crew Type 2500
Human-Machine Interface; Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance; Flight Crew Became Reoriented; Flight Crew FLC complied w / Automation / Advisory
Human Factors
We setup and briefed the copilot's approach to RNAV 4L into Boston Logan airport. Leveled off at final approach intercept altitude using the autopilot. Set next altitude in altitude preselect. On final approach; we entered VMC conditions the copilot looked at the GPS to verify our position related to the FAF. I was looking outside for traffic as we were VMC. He believed to be over the FAF and began to descend. ATC issued a low altitude alert and we immediately leveled off. ATC asked if we had the runway and traffic to follow in sight to which we replied; yes we did. ATC then cleared us for the visual approach which continued without incident.
Air carrier Captain reported an excursion from cleared altitude resulting in a low altitude warning. The crew corrected the deviation and landed without incident.