Fractional flight crew and helicopter pilot reported a NMAC with each other in the traffic pattern. Helicopter pilot turned base leg in front of the fractional aircraft and then turned directly toward them during final approach.
Synopsis
Fractional flight crew and helicopter pilot reported a NMAC with each other in the traffic pattern. Helicopter pilot turned base leg in front of the fractional aircraft and then turned directly toward them during final approach.
Narrative
My co-pilot and I were operating a flight from ZZZ1 to ZZZ. Neither pilot had prior experience at this airport. Given that it is an uncontrolled field with a high volume of mixed general aviation traffic; we conducted a thorough arrival briefing on the ground and again in flight to mitigate perceived risk.Approximately 30 NM south of the airport; the Captain (Pilot Monitoring) began making CTAF position reports and advising traffic of our plan to overfly midfield and enter a left downwind for Runway XX. This plan was also communicated to ZZZ [TRACON]; with whom we were still in contact and receiving vectors.Upon crossing midfield at approximately 3;000 feet MSL; I remained on the ZZZ [TRCAON] frequency and assumed ATC communications; while the Captain switched to COM 2 on CTAF to continue traffic advisories and monitor pattern activity. ATC vectored us onto a left downwind and subsequently issued a turn to left base approximately five miles from the field. After reporting the field in sight; we were cleared for a visual approach. At that point; we canceled IFR and both pilots transitioned to CTAF.During the turn to final; we began a descent toward Runway XX. The autopilot remained engaged; coupled to the RNAV approach for backup lateral and vertical guidance during the visual approach. The Captain advised that a piston fixed-wing aircraft and a helicopter had reported on downwind and stated their intention to follow us. I had heard the fixed-wing aircraft's radio calls but did not hear a helicopter transmission and did not have visual contact with either aircraft.At approximately 1;000 feet AGL; we received a TCAS traffic alert indicating traffic at the same altitude; converging head-on. I immediately disconnected the autopilot. Both pilots then acquired visual contact with the helicopter. I initiated a slight left turn; and the Captain instructed me to continue descending; which I did. The helicopter passed off our right wing at extremely close proximity.Based on ADS-B playback and track log data from both aircraft; we estimate lateral separation of approximately 700-1;200 feet. Given the relative closure rate; I believe the time to closest point of the two aircraft colliding was less than three seconds; representing a serious near mid-air collision hazard.Following the encounter; I stabilized the approach and we landed without further incident. While back-taxiing after landing; we observed the helicopter again on short final for Runway XX.Approximately 20 minutes after landing; the helicopter was observed being towed on a trailer past our aircraft. We flagged the pilot down and asked for clarification regarding the event. When asked how he came to be head-on with us on final; the pilot appeared irritated and stated that he did not expect us to extend that far" in the pattern.We explained that ATC had vectored us to that position and that the pattern size was typical for a jet aircraft. We also stated that he had announced his intention to follow us. The helicopter pilot was unable to clearly articulate his decision-making process in the pattern or explain why he turned inside of our base-to-final turn.Review of publicly available ADS-B track data shows the helicopter crossing midfield at approximately 70 knots and 400 feet AGL; entering a left downwind at the same time we were turning left base. The helicopter then climbed to approximately 900 feet AGL while beginning a dogleg toward final. He subsequently turned left base inside of our position and; seconds later; made an unexplained right turn that placed him directly on a head-on collision course with our aircraft at the same altitude on final approach to Runway XX.The helicopter then turned left out of the final approach course; passing in front of us and off our right wing; slightly above our altitude; with an estimated lateral separation of 700-1;200 feet."
Second reporter narrative
Arriving to ZZZ from ZZZ1. Started listening to Unicom approximately 30-35 miles out and heard multiple calls for traffic operating at ZZZ. At 25 miles to south and at 9000' I made our first position report with our intentions to over fly the airfield at 2000' and enter left downwind for runway XX. 2nd position report was about 10 miles to the south at 5000' reporting our same intentions. I heard one report of single engine departing to stay in left traffic. Due to the heavy volume of chatter on both the ATC ZZZ [TRACON] and the ZZZ Unicom; I opted to monitor the Unicom and my FO was monitoring ATC as we did not have the field in sight yet. Next position report was over the airfield at 3000' starting our descent to traffic pattern of 1600' and single engine aircraft reported they were going to follow us. Next position report was left down wind for runway XX. I heard a report of a helicopter to the south asking our position. This was Aircraft Y and I reported NW of the airport on the left downwind. I heard the helicopter report they were going to follow the single engine aircraft to runway XX. My next report was left base; and then reported turning final for runway XX. I'd estimate we turned final just inside of 5 miles and we had the runway insight. We were fully configured and began descent to runway XX. At approximately 1000' we got a TCAS caution traffic that showed up directly in front of us. We then saw the helicopter and I asked to keep descending and we turned slightly left and the helicopter appeared to also continue to move across the final approach path from our left to right and passed off our right side slightly above us. We think the near miss was within 1000-1500'. We were able to continue the stabile approach and land without incident to runway XX at ZZZ. I was able to find and speak with the pilot of the helicopter and he just kept saying he didn't know we were going so far out on the downwind leg as no one does that at this airport. I told him we reported our positions and turned inside a 5 mile final. I never got an answer as to why he ended up on the final approach course directly in front of of us.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.