Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 100; Flight Crew Total 3100; Flight Crew Type 100
Distraction; Situational Awareness
Deviation - Altitude Overshoot; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Human Factors
Myself and my Captain were flying our final leg from ZZZ to HWD. Conditions were night VMC and we had the Hayward city and airport location in sight. The Captain was pilot flying and I was pilot monitoring. The Captain was manually flying and our clearance was to maintain 4;000 until established on the localizer. I went into my iPad to look at my charts; a few moments later I heard the Controller tell us; 'low altitude alert; check altitude immediately; MVA is 3;900.' When I looked over at the Captain's PFD; I saw we had descended to between 3;300-3;400 feet. The Captain took over the radios and corrected the altitude and continued uneventfully.
Light Transport aircraft First Officer reported a CFTT event during approach to HWD airport.  The crew immediately corrected after ATC made them aware of the issue.