Date: 202101
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: IMC
Light: Daylight
Aircraft: Regional Jet 900 (CRJ900)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class C ZZZ
ATC / advisory: TRACON ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown; Workload; Training / Qualification; Situational Awareness; Human-Machine Interface
Second reporter function: Pilot Flying; First Officer
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Detector: Automation Air Traffic Control; Automation Aircraft Other Automation; Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Flight Crew FLC complied w / Automation / Advisory
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: ATC turned us onto the approach while still at 4;000. Told us to 'maintain 3;000 till established cleared ILS [Runway] XXL. FO (First Officer) put in 3;000 in the altitude selector and I acknowledged it. Once established; instead of selecting 2;700 feet for the FAF altitude he rolled the altitude selector to 3;300 and started a slow descent. Stated he was going to just control the altitude himself. I thought that was strange; but let him do it figuring it was just a technique he liked to do.As we approached 2;700 feet; he was still descending at ~700 FPM; so I realized he was going to blow through the altitude. I told him he needed to stop descending and return to the FAF altitude until we intercepted the GS. The first time I said this he seemed confused and didn't really do much. I said more sternly that we needed to climb back to the proper altitude. This time he initiated a climb back to the proper altitude and we were still stabilized and fully configured by 1;000 feet AGL. ATC did issue us a low altitude alert as we were climbing back to the proper altitude and we got a single 'Glideslope' callout from the aircraft.The cause was the FO's improper use of the altitude selector and VS (Vertical Speed) mode. Contributing was me allowing him to do the method he did instead of asking him to just put the FAF altitude in the altitude selector till GS intercept.I should have insisted that the FO put the FAF altitude in the altitude selector; especially in IMC. I also told him afterword's that he could have just stayed at 3;000 once established and intercepted the GS from there since at that point we were already close to GS intercept.


Second narrative: Cleared ILS [Runway] XXL; we were given an intercept heading and told to maintain 3;000 feet. The Controller kept us close and fairly high before clearing us for the approach. We were at 4;000 feet when cleared. Captain was PM (Pilot Monitoring); First Officer was PF (Pilot Flying). Once established; PF started down with vertical speed to capture glide slope by 2;700 feet at ZZZZZ. PF moved altitude knob up to 3;300 feet from 3;000 feet instead of to 2;700 feet causing us to go below published altitude by almost 500 feet. Was immediately corrected and aircraft was stabilized. Given a close proximity intercept; task saturation was high with intercepting; radio communications; and configuring aircraft. Should have cross checked better and stated intentions more clearly (PF to PM).If crew starts to feel rushed or task saturation is high; ask for longer final or a more stable intercept from ATC. Never let cross checking suffer due to task saturation; should always come first. PM should state approach intention more clearly while getting established. Don't have tunnel vision (Example Focusing on getting configured and not having correct altitude set).


Synopsis: CRJ-900 flight crew reported receiving a Low Altitude Alert from ATC after they descended below the glideslope intercept altitude.