I know I’m late to the game here, but I just wanted to relate some R2800 experience first hand. After watching the video a couple of times, what happened is definitely a “choke out” of the #1 and #4 engine when the crew held the engines in reverse too long and allowed the aircraft to almost stop while in reverse. R2800’s are very sturdy engines, but they are also fickle about running in “dirty” air. I don’t know if this DC-6 was equipped with dust filters or not, but if it wasn’t, then it’s not hard to cause this problem. It is also interesting to note that the #2 engine “sticks” in reverse (happens sometimes with the Hamilton prop, never got a good explanation for why) and the crew probably had to cycle the feather pump a couple of times to “bump it over” and get it going the right way. My first-hand experience is with the CV-240, but the reversing method/mechanism is the same between the two aircraft, and it was always interesting to do ground reverse tests because the airflow was so badly disrupted when the aircraft was not moving as to cause the engine to be seriously starved of air during the “flat” portion of the transition and would occasionally cause pretty spectacular backfires (and occasionally cause the engine to quit completely). It occasionally happened during landing too if you had a slight tailwind (definitely a pucker factor if you were on a short runway and heavily loaded like it was the time it happened to the crew I was flying with). As you’re landing anyway, it was never a “major” problem, but it definitely wasn’t something you planned to do, it’s just the physics of reversing the big fan that’s feeding the engine air. 🙂