Air carrier flight crew reported a RA while on initial approach into LGA. Flight crew complied with RA and reported NMAC to ATC.
Synopsis
Air carrier flight crew reported a RA while on initial approach into LGA. Flight crew complied with RA and reported NMAC to ATC.
Narrative
We received an RA during our arrival and approach at LGA while leveled at 4000ft MSL and flying the GGREG transition on the RNAV (GPS) X RWY 31 approach. As we were approaching the JACIE intersection; ATC notified us of an airplane that was descending above us and leveling off at 4500ft MSL. We looked for the airplane and maintained visual contact both outside and on TCAS as it descended to its assigned altitude; 500ft above our assigned altitude of 4000ft MSL. As the plane leveled off and flew passed above us; we received an RA directing us to Monitor Vertical Speed". We immediately followed procedure; complied and maintained our altitude since the command was to not ascend onto said traffic (no evasive action needed). Once the conflicting traffic was no longer a factor; the RA went away; we reengaged the autopilot and notified ATC about it. The rest of the flight went without incident.Cause: Airplane descending in close proximity to us (500ft) causing an RA. Wind gusts/turbulence causing small altitude deviations by the small airplane above us could have been a contributing factor.Suggestions: We could have been given/requested a vector away from the airplane to prevent a possible RA when maintaining 500ft of vertical separation."
Second reporter narrative
On the RNAV (GPS) X RWY 31 in to LaGuardia Airport after JACIE we received a TCAS RA monitor VS due to an Aircraft Y dropping below +500 feet above us momentarily to +400 feet above us. We were informed by approach of the Aircraft Y descending from 5;000 to 4;500 feet in which I replied looking for traffic and Aircraft Y advised Approach they had our aircraft insight. I soon after responded that we had Aircraft Y in sight as well. It was then when we received the TCAS RA after JACIE. Our altitude at the time was 4;000 feet with the autopilot on and engaged Captain's side and the Aircraft Y was supposed to be at 4;500 feet. We were watching the Aircraft Y on our radar and responded appropriately the TCAS RA as it occurred immediately. Cause: I believe it was just simply the timing between Aircraft Y passing over us and unintentionally descending below their assigned altitude of 4;500 feet triggering our TCAS RA. It could have been turbulence/weather that was a factor in the cause of this; but that is only my opinion.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.