Narrative:

I was performing OJT (on the job training) instruction with my developmental (deviation) who is on his second set of radar sectors. He accepted the hand off on aircraft X from hnn at FL360 inbound to lex. Once the aircraft called on; my deviation descended him to FL350. My deviation then accepted a hand off on an aircraft; aircraft Y; about 40 miles west of aircraft X converging at FL360 landing iad. There was a tmu message out requiring iad arrivals at or below FL330 entering ZDC airspace. Aircraft X was level at FL350 at the time. My deviation then cleared aircraft X to descend to FL240. Once he had observed aircraft X leaving FL350; he issued descent clearance to aircraft Y to FL350 in accordance of 7110.65 paragraph 5-5-5b. The two aircraft were still 25 miles apart converging when this descent clearance was issued. A minute or so later; aircraft Y advised he was alerted to climb 300 feet by his TCAS. Deviation then called the traffic to the aircraft Y. Aircraft passed each other and aircraft Y returned to FL350.a prescribed standard rate of descent amongst all turbojet aircraft would have prevented this occurrence. The aircraft X; with performance characteristics very similar to aircraft Y; descended at only 500 feet per minute whereas the aircraft Y descended at about a 1500 feet per minute rate. This was the pilot's choice without advising ATC. Had the aircraft X maintained a very reasonable 1000ft per minute rate; aircraft Y would never had received an RA from TCAS and the event would not have occurred.

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Original NASA ASRS Text

Title: ZID instructor reports of his developmental descending aircraft using the vacated altitude rule; which led to a loss of separation.

Narrative: I was performing OJT (On the Job Training) instruction with my developmental (DEV) who is on his second set of radar sectors. He accepted the hand off on Aircraft X from HNN at FL360 inbound to LEX. Once the aircraft called on; my DEV descended him to FL350. My DEV then accepted a hand off on an aircraft; Aircraft Y; about 40 miles west of Aircraft X converging at FL360 landing IAD. There was a TMU message out requiring IAD arrivals at or below FL330 entering ZDC airspace. Aircraft X was level at FL350 at the time. My DEV then cleared Aircraft X to descend to FL240. Once he had observed Aircraft X leaving FL350; he issued descent clearance to Aircraft Y to FL350 in accordance of 7110.65 paragraph 5-5-5b. The two aircraft were still 25 miles apart converging when this descent clearance was issued. A minute or so later; Aircraft Y advised he was alerted to climb 300 feet by his TCAS. DEV then called the traffic to the Aircraft Y. Aircraft passed each other and Aircraft Y returned to FL350.A prescribed standard rate of descent amongst all turbojet aircraft would have prevented this occurrence. The Aircraft X; with performance characteristics very similar to Aircraft Y; descended at only 500 feet per minute whereas the Aircraft Y descended at about a 1500 feet per minute rate. This was the pilot's choice without advising ATC. Had the Aircraft X maintained a very reasonable 1000ft per minute rate; Aircraft Y would never had received an RA from TCAS and the event would not have occurred.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.