tcas ra's
I was working two days ago. Had two a/c, one climbing, one descending, nose to nose, with 1000 ft. vertical assigned ( the right way) and acknowledged. Passed traffic to both a/c. When a/c were approx. 5nm nose to nose, descending a/c, about 300 ft above cleared level, had an RA.
He announced TCAS climb, but only climbed about 100 ft, before announcing he was resuming ATC cleareance. The opposite direction climbing a/c did not get an RA. Climbing a/c was within 200 ft. of his cleared level.
I have been told by pilots, and assumed, when traffic is passed in similar cases, pilots decrease their vertical rates to avoid RA's.