Date: 201808
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Second aircraft: Skyhawk 172/Cutlass 172
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Situational Awareness
Anomaly: Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Detector: Automation Aircraft Terrain Warning; Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Provided Assistance; Flight Crew Took Evasive Action; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Airspace Structure; Human Factors; Environment - Non Weather Related
Primary problem: Human Factors

Narrative: Flying the visual [to] Runway XX at ZZZ. Following the charted points of ZZZZZ; ZZZZZ1; AND ZZZZZ2. Approaching ZZZZZ1 in the turn; ZZZ Tower advised us to square off our base for a Cessna 172 flying an approach to the crossing Runway XY. As Pilot Flying; I was following the advisory snowflake at 1200 feet and in the turn to final when I rolled back to the left to square off the turn and turn away from the runway. Unfortunately; I continued to descend and reference the VNAV snowflake not realizing that it was tracking their descent off azimuth. At 800 feet; I corrected with a generous amount of power as ATC announced a low altitude alert and told me to check my altitude. ATC stated my altitude over the estuary was 700 feet. After correcting back to 1200 feet; we were cleared to rejoin Runway XX final; but not given landing clearance until a 2 mile final; whereupon the crossing traffic Cessna 172 was told to go around. If I had followed the approach as published; this would not have happened. I should have realized the moment I had to turn away from the runway that I would have to stop my descent and no longer follow the advisory VNAV guidance. Simultaneously; my First Officer was clearing traffic; since the runway was on his side of the aircraft and called for me to stop my descent. The descent was very gradual; so it didn't immediately get the First Officer's attention. The subsequent landing was uneventful.First Officer alerted; [then] followed closely by air traffic controller giving us the low altitude alert. [The cause was the] requirement to extend pattern after cleared for visual approach during turn to final. Controller given priority to GA slower aircraft. Added power and corrected back to pattern altitude. ATC initially asked us to 'KEEP OUR SPEED UP' then handed us off to a Tower with three jets going to Runway XX and a Cessna 172 going to the crossing Runway XY. Maybe have the Cessna break off the approach and let the jets land first next time.




Synopsis: CRJ-200 Captain reported a low altitude alert after continuing to descend while extending final for traffic landing on crossing runway.