Date: 201705
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Night
Aircraft: Helicopter
Operator: Government
Operating under: Part 91
Flight plan: None
Flight phase: Cruise
Airspace: Class C ZZZ; Class E ZZZ
ATC / advisory: Tower ZZZ; UNICOM ZZZ
Second aircraft: Helicopter
Reporter organization: Government
Reporter function: Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument
Human factors: Time Pressure; Workload; Situational Awareness; Confusion; Communication Breakdown; Distraction
Anomaly: Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew; Person Observer
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Airspace Structure; Environment - Non Weather Related; Human Factors; Procedure
Primary problem: Procedure

Narrative: At approximately XA46; Aircraft X and Aircraft Y responded to a stranded hiker. After approximately 20 minutes of searching low level in the canyon; we located the stranded hiker and hoisted our rescuer down for patient care. After hoisting the rescuer down; we repositioned into a 60-knot right orbit between the rescue site and the Freeway awaiting Aircraft Y's command to come back in for the rescue. After about 5 minutes; Aircraft Y called us back in to the rescue site to retrieve our rescuer; so we rolled into a north bound turn from our holding orbit. As I rolled out; I looked up and to the right and saw a night sun equipped aircraft converging above and to the right which I believed to be Aircraft Y in a right-hand orbit. During the next couple seconds; I began a descent with what I believed was Aircraft Y 'in-sight' and noticed the night sun beam rapidly sweeping towards us. I continued our north bound descent as the night sun beam hit our aircraft and swept through the cockpit from what I believed was Aircraft Y passing overhead.At this point; the co-pilot and safety member in the right rear cabin area also had eyes on the converging aircraft. We all estimated our altitude separation to be approximately 300' as the converging aircraft passed overhead. While a 300-foot altitude separation is not uncommon between hoist and firefighting aircraft that are in communication with each other; this incident should be considered a near miss as the aircraft involved were in close proximity but not in communication. Because of the initial rescue site being in [a] tower controlled airspace; we were not monitoring adequately for any traffic advisories in the area. Both rescue aircraft were monitoring the tower frequency intermittently; air-to-air; and the rescue tactical. As always; there was task saturation with the combination of rescue briefings in the aircraft; radio traffic with the ground companies and air traffic control during the rescue. Aircraft typically monitors [traffic advisories] but also became task saturated while developing a rescue plan with the incident commander on the ground. It's also likely that while we were in [the Class C] airspace at the rescue site and monitoring their frequency; we were out of radar contact due to the obstruction of [the mountain]. Immediately after the near miss; the co-pilot of the rescue broadcast on [traffic advisory frequency] that Aircraft Y and Aircraft X were working in the [mountain] area below 1700 feet for any media ships that might be in the area. What we think was Aircraft Z responded that they were near the Freeway.Contributing factors to the near miss event:* We did not have TCAS displayed on the co-pilots MFD of the rescue aircraft which would have alerted us to the converging aircraft. * My misidentification of the rescue aircraft as 'Aircraft Y' with a night sun; resulted in my comfort in passing below; what I thought was Aircraft Y; rather than executing evasive maneuvers. * Once we moved south from the rescue site; we were out of class C airspace and should have monitored/ self-announced [our position].* Because the rescue site was on the boundary of the southern edge of [the Class C] airspace; both rescue aircraft were monitoring [tower] but not [common traffic frequency]. Even though we are engaged in high risk hoist rescue operations in the mountains and foothills at night; we need to continue to be vigilant in assigning one of the pilots in either the rescue aircraft or the rescue aircraft the task of monitoring [common traffic frequency]. Any aircraft on scene should also have the TCAS selected to the co-pilots MFD to help with early identification of traffic conflicts.




Synopsis: Rescue Helicopter pilot reported a near miss at night with what the crew thought was an accompanying aircraft. In reality was an unidentified aircraft.