Date: 201808
Local time of day: 1201-1800
Location: ZSHA.ARTCC, FO
Flight conditions: Mixed
Weather elements / visibility: Thunderstorm
Aircraft: Widebody Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
ATC / advisory: Center ZSHA
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Check Pilot; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Commercial; Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface; Situational Awareness; Communication Breakdown
Second reporter function: First Officer; Pilot Flying
Anomaly: ATC Issue All Types; Conflict NMAC; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft RA; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Contributing factors: ATC Equipment / Nav Facility / Buildings; Airspace Structure; Human Factors; Weather
Primary problem: Human Factors

Narrative: The departure was normal with a non-typical flight routing to the north due to weather off the coast. We began the flight in trail of other aircraft all using the same routing which resulted in a low initial cruise flight level followed by small incremental step climbs. We were flying an assigned right offset of 6 miles. Just prior to the event; we were given a climb from 10;100 meters to 10;400 meters. As we reached 34;100 feet; we were assigned a right 5 mile offset which the Pilot Flying entered into the FMC in a timely manner; but I am not certain if it had been executed prior to the beginning of the event. The event began when the ATC controller (in a somewhat stressed voice) told us to turn left to a heading of 270 (about a 90 degree left turn).I immediately reached to the HDG SEL knob and twisted it left and pushed the button to begin the turn. While we began our turn; ATC gave the conflicting aircraft a left turn as well. We then received a 'Traffic Traffic' alert on TCAS. As I looked down at the ND display we had an amber traffic superimposed on top of our airplane symbol with '0' indicating it was at our altitude. My Navigation Display scale was set at a larger scale so it was difficult to establish the separation distance accurately. At this time; the First Officer (Pilot Flying) turned his scale down to a low range and from the right side of the aircraft [and] was able to acquire the conflict visually. The Pilot Flying then disconnected the autopilot and increased the bank angle from the HDG SEL 15 or so degrees bank to approximately 30 to 35 degrees in an effort to increase our turn rate and decrease our turn radius. The TCAS display soon showed the conflicting aircraft to be 100 feet below our altitude. At this point; I placed my hands on the yoke and decreased the bank angle to 20-25 degrees and increased backpressure to achieve a slight climb rate as we had descended slightly in the turn. No resolution advisory (RA) of TCAS was issued. Once clear; we then rolled wings level and reengaged the autopilot in HDG SEL and VNAV ALT at 34;100 feet. We then asked for and were given direct routing to the next point on our route and where a frequency change was then made.The airspace had an abnormally high level of congestion due to a weather system off the coast. ATC communication transmissions were of very poor quality (over modulation and distortion) resulting in many missed and/or repeated transmissions. The ATC system was obviously saturated and overloaded. I believe that the controller had descended the conflicting aircraft through our altitude failing to provide adequate separation considering the closure rate of the two nose to nose aircraft. The poor quality of his transmitter required him to make additional transmissions which diverted his attention. He was obviously overloaded at the time and not able to keep track of all the aircraft he was responsible for.


Second narrative: [Report narrative contained no additional information.]


Synopsis: Air carrier flight crew reported a NMAC with opposite direction descending traffic while deviating for weather.