Date: 201810
Local time of day: 0601-1200
Location: MUFH.ARTCC, FO
Flight conditions: VMC
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
ATC / advisory: Center MUFH
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Workload; Communication Breakdown; Situational Awareness
Second reporter function: Pilot Not Flying; First Officer
Anomaly: ATC Issue All Types; Conflict NMAC
Detector: Automation Aircraft RA; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: At FL360 over Cuba flying northbound; my FO (First Officer) was leaving the cockpit on a restroom break before our planned descent when Havana Center began issuing instructions 'for spacing.' I understood a left turn to heading 330 which was approximately a 50 degree west course change. I asked the Controller four times to repeat the rest of the clearance. He was extremely difficult to understand; and I thought he was either telling me about traffic at FL350 (which might explain the hard spacing turn); or maybe he was telling me to descend to FL350. I started looking for an airplane visually. Also the cockpit exchange was happening and the Flight Attendant settled in behind me with questions about our arrival time. After repeatedly questioning the Controller; Havana Center eventually told me to descend to FL320 and something about 1;000 feet per minute. Without being able to understand every word of his clearances; I assumed he wanted at least 1;000 feet per minute so he could turn me back on course at a new lower altitude. At this point I'm flying single pilot on autopilot with the oxygen mask while trying to visually spot traffic. I dialed in FL320 and pressed Flight Level Change. I was too busy to program VNAV; and I don't like using Vertical Speed at high altitude because it doesn't offer speed protection. At approximately 32;800 feet I received an RA warning on my TCAS. I immediately disconnected the autopilot and leveled the airplane. My co-pilot felt the abrupt level off from the forward lavatory and began calling the cockpit shortly thereafter. It was then that I saw the other aircraft right below me and barely a wing span to my left just appear from under my aircraft. I broadcast my level off and the RA warning to the Controller who incredulously told me to continue descent to FL300; and something about the other aircraft also descending at 1;000 feet per minute. In the moment; considering the Controller had turned me off course and on top of the other aircraft and then issued not just a descent; but further descent even after the RA began; I felt he was deliberately trying to make our airplanes collide. I refused to continue descent and he continued with his 1;000 feet per minute explanation. At some point [another] controller took over; hopefully a supervisor; who handled our aircraft briefly then handed us over to Miami Center.I have been flying commercial aircraft for over 30 years and I have never had a controller deliberately stack two aircraft and then issue a simultaneous clearance to descend through the same altitudes and expect the descent rate to keep them apart. That's what I think he tried to do in retrospect. In the moment; even deciphering his English was a huge challenge (and I'm semi-fluent in Spanish). It is my experience that aircraft are to be given hard altitude separation and stepped down appropriately; or turned and given lateral separation. It appears this Havana Controller removed lateral separation with his vectoring; and then removed vertical separation by issuing descent clearances through common altitudes.


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


Synopsis: B737-800 flight crew reported an NMAC in Havana airspace due to language difficulties and poor descent instructions.