Narrative:

I received handoffs on 2 departures from san antonio approach control. Medium large transport X was in the lead, medium large transport Y was the succeeding departure. Both aircraft were filed the same route as far as elp. Medium large transport X was requesting FL330. Medium large transport Y was requesting FL250. When I received handoffs on these flts they were altitude separated with between 4-5 mi latitude. I climbed medium large transport X to FL230 and asked what his rate of climb would be. He advised 2000 FPM, and I instructed him to maintain 2000 FPM in the climb. Medium large transport Y checked on frequency level at 13000', advised medium large transport Y that he was stuck under another departure on the same route, and that if he could maintain 1000 FPM in the climb he would not have to level off. I assigned medium large transport X FL330 and to maintain 2000 FPM through FL230. Pilot concurred. I observed the climb rates of both aircraft to ascertain that my plan was working. I then assigned medium large transport Y FL230 and advised that FL230 would be his final altitude. When I next observed the altitude readouts, medium large transport X was leaving FL211 and medium large transport Y was leaving FL195. My plan was no longer working, but I still had 1600' sep. I advised medium large transport Y to maintain FL200, thinking that he would have no problem leveling since he was climbing at 1000 FPM. The next altitude update showed medium large transport X leaving FL210 medium large transport Y leaving FL202. I asked medium large transport Y to say altitude. He replied, 'we're descending to FL200, we were at it when you called.' the next altitude update showed medium large transport X leaving FL214, medium large transport Y FL206. Medium large transport Y then reported reaching FL200.

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Original NASA ASRS Text

Title: SEPARATION WAS LOST BETWEEN 2 CLIMBING ACFT TO ASSIGNED ALTS.

Narrative: I RECEIVED HDOFS ON 2 DEPS FROM SAN ANTONIO APCH CTL. MLG X WAS IN THE LEAD, MLG Y WAS THE SUCCEEDING DEP. BOTH ACFT WERE FILED THE SAME RTE AS FAR AS ELP. MLG X WAS REQUESTING FL330. MLG Y WAS REQUESTING FL250. WHEN I RECEIVED HDOFS ON THESE FLTS THEY WERE ALT SEPARATED WITH BTWN 4-5 MI LAT. I CLBED MLG X TO FL230 AND ASKED WHAT HIS RATE OF CLB WOULD BE. HE ADVISED 2000 FPM, AND I INSTRUCTED HIM TO MAINTAIN 2000 FPM IN THE CLB. MLG Y CHKED ON FREQ LEVEL AT 13000', ADVISED MLG Y THAT HE WAS STUCK UNDER ANOTHER DEP ON THE SAME RTE, AND THAT IF HE COULD MAINTAIN 1000 FPM IN THE CLB HE WOULD NOT HAVE TO LEVEL OFF. I ASSIGNED MLG X FL330 AND TO MAINTAIN 2000 FPM THROUGH FL230. PLT CONCURRED. I OBSERVED THE CLB RATES OF BOTH ACFT TO ASCERTAIN THAT MY PLAN WAS WORKING. I THEN ASSIGNED MLG Y FL230 AND ADVISED THAT FL230 WOULD BE HIS FINAL ALT. WHEN I NEXT OBSERVED THE ALT READOUTS, MLG X WAS LEAVING FL211 AND MLG Y WAS LEAVING FL195. MY PLAN WAS NO LONGER WORKING, BUT I STILL HAD 1600' SEP. I ADVISED MLG Y TO MAINTAIN FL200, THINKING THAT HE WOULD HAVE NO PROB LEVELING SINCE HE WAS CLBING AT 1000 FPM. THE NEXT ALT UPDATE SHOWED MLG X LEAVING FL210 MLG Y LEAVING FL202. I ASKED MLG Y TO SAY ALT. HE REPLIED, 'WE'RE DSNDING TO FL200, WE WERE AT IT WHEN YOU CALLED.' THE NEXT ALT UPDATE SHOWED MLG X LEAVING FL214, MLG Y FL206. MLG Y THEN RPTED REACHING FL200.

Data retrieved from NASA's ASRS site as of July 2007 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.