Date: 202110
Local time of day: 1201-1800
Location: N90.TRACON, NY
Weather elements / visibility: Icing; Turbulence
Light: Daylight
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B EWR
ATC / advisory: TRACON N90
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Situational Awareness
Second reporter function: Captain; Pilot Not Flying
Anomaly: Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Detector: Automation Air Traffic Control; Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: On approach into LGA we were being vectored for the ILS 4 and were soon cleared for the approach to maintain 2;000 ft. until established. We were intercepting the FAC between DINNS (the FAF; min alt 1;700 ft.) and GREENE (the IF; min alt 2;700 ft.). Once we were cleared for the approach I selected 1;700 ft. in the altitude selector for the FAF altitude and we were descending from 3;000 in FLCH. Passing through 2;000 ft. I was aware of my mistake and selected 2;000; in the altitude selector causing the airplane to continue to descend in FPA. In the process we ended up descending to 1;600 ft. at which time I disengaged the AP and immediately corrected the situation. However; a low altitude alert was issued at this time and the approach continued without further incident. I will ensure the ATC clearance is adhered to even if I am cleared for the approach. Additionally; I would recommend placing an additional emphasis on verifying AP modes.


Second narrative: Cleared to maintain 2;000 ft. until established; then cleared ILS 4 at LGA. I was PIC acting as non flying pilot. Flying pilot placed 1;700 ft. in ALT Select window (which was the FAF altitude) with the intent to intercept glideslope prior to final approach fix. I reiterated the last clearance was for maintain 2;000 ft. until established. At this point; flying pilot attempted to reset altitude selector to 2;000 ft. but the autopilot at this point was already in ASEL mode hence it reverted FPA mode and descent below 2;000 occurred before flying pilot made a smooth but aggressive correction back to 2;000 ft.. Altitude deviation was approximately to 1;700 ft. before corrected to 2;000 ft. The flying pilot then intercepted glideslope at the correct altitude of 2;000 ft. remaining ILS in VFR conditions was hand flown by flying pilot without incident. All this occurred as I checked on to Tower frequency and was met with a low altitude alert warning from Tower Controller upon check in and asked to recheck altimeter setting. I acknowledged; landing clearance was then obtained and we proceeded without incident. We were in VMC conditions and ground contact was never a threat or concern and I consider the event a momentary deviation with positive correction though it did cause an altitude deviation. As PIC; I felt the flying Pilot was situationally aware; made a timely correction to his mistake; thereby not requiring further intervention on my behalf. Dial in the correct altitude in the first place as per Controller instructions.


Synopsis: Pilots reported entering an incorrect altitude; catching it; but the aircraft continued descending; resulting in a low altitude alert from ATC.