ACR X NON ADHERENCE TO ATC CLRNC CLB THROUGH OCCUPIED ALT HAD LTSS FROM ACR Y. SYS ERROR. PLTDEV.

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ACFT INVOLVED WERE ACR X; AN A-320; DEPARTED MSP ENRTE TO PHX AND ACR Y. ACR X REQUESTED TO CLB FROM FL350 TO FL390. I CLBED ACR X TO FL390. I OBSERVED ACR X MODE C CLB RATE TO DECREASE CONSIDERABLY AND THEN STOP AT FL385. ACR Y WAS NEBOUND AT FL370. ACR X WAS ASKED IF HE COULD BE LEVEL IN 1 MIN. HE REPLIED IN THE AFFIRMATIVE AND I INSTRUCTED ACR X TO RPT LEVEL FL390. I OBSERVED NO CHANGE IN THE MODE C ON THE NEXT RADAR UPDATE AND IMMEDIATELY TURNED ACR Y 30 DEGS R; HE ACKNOWLEDGED. I THEN TURNED ACR X 30 DEGS R; HE ACKNOWLEDGED AND THEN STATED THAT HE WOULD HAVE TO SLOW DOWN THE CLB. CLOSEST PROX WAS 3 MI AND 1500 FT. WHY ACR X STOPPED AT FL385 IS UNKNOWN. IT IS MY UNDERSTANDING; AS TOLD BY ANOTHER EA-320 PLT; THAT A STANDARD CLB RATE FROM FL350 TO FL390 WOULD BE 700 FPM. AT THIS RATE; ACR X SHOULD HAVE BEEN LEVEL WITHIN 5 TO 6 MINS. IT TOOK ACR X OVER 7 MINS BEFORE RPTING LEVEL. IT IS MY OPINION THAT ACR X WAS NOT CLBING AT AN OPTIMUM RATE. PARAGRAPH 4-89D OF THE AIRMAN'S INFO MANUAL STATES THAT A PLT SHOULD ADVISE ATC IF HE CANNOT CLB AT AN OPTIMUM RATE.