A319
Flight Crew Air Transport Pilot (ATP)
Flight Crew Type 797
Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Human Factors
During the approach brief; the Captain was the pilot flying and briefed the LDA-A for Runway 22 at LGA. At the end of his brief; due to the VFR weather at the destination; he mentioned that in the end; it would probably be a visual approach to Runway 22 at LGA. During the brief; it was difficult to understand him; but being aware of what a brief consists of; I did not press him on it; and the flight continued.While on final vectors; the pilot flying (Captain) entered a visual descent point fix into the FMGC off of runway centerline; and mentioned to me what he was doing; which seemed different; but having never seen the LDA-A into LGA; I didn't question it; believing he had a technique he liked to use after having done the approach over the years. As we were vectored to intercept the LDA inbound course; we were cleared to 'maintain 1;600 until COHOP; cleared for the LDA-Alpha; Runway 22'. As the Captain intercepted the inbound course; he disconnected the autothrust and autopilot; and hand flew the aircraft at 1;600 feet. The navigation display showed a line from a now frivolous visual descent point on runway centerline to Runway 22; which was initially confusing; since the LDA approach is offset to the left; however; the localizer was hard-tuned and indicated we were on course.With the FAF (COHOP) depicted at 5.2 NM; the Captain began a descent at roughly 6.3 NM; with the runway visually in sight. This caused confusion for me; as I had just read the approach clearance back to the controller that we were cleared for the LDA-A approach and not the visual. Thinking I may have missed something or set my navigation instruments wrong; I began cross-checking my displays to the approach plates; and cross-checked that both pilots instruments were set correctly and reading the same. From a visual standpoint looking out the windscreen; the late afternoon sun had a blinding glare off of the water; which made it difficult to properly see the PAPI from that distance to verify the glide slope. However; checking the approach plate to the indicated DME; it was apparent the descent was early.As I was finishing my re-checks; the Captain requested that track/Flight Path Angle (FPA) be set to 3 degrees for a glide slope down final approach. I began to set it; but queried the Captain as to why he was descending with the final approach fix still some distance away; to which he mentioned that he had the runway visually. I also mentioned that looking out the windscreen; it appeared that we were low; and suggested a level-off as opposed to a continued descent; with COHOP still not having been reached. At this point; I recall seeing about 900 feet MSL on the altimeter; and LGA Tower called to notify us that he had received a low altitude warning for us. I acknowledged his call; and the Captain initiated a climb that put the aircraft back on a normal profile for landing. The remainder of the approach to landing was uneventful.
A319 FO reported the flying pilot (the Captain) descended early on the LDA-A approach to LGA; prompting a low altitude alert call from ATC.