Narrative:

Aircraft involved were air carrier X, an A-320, departed msp en route to phx and air carrier Y. Air carrier X requested to climb from FL350 to FL390. I climbed air carrier X to FL390. I observed air carrier X mode C climb rate to decrease considerably and then stop at FL385. Air carrier Y was nebound at FL370. Air carrier X was asked if he could be level in 1 min. He replied in the affirmative and I instructed air carrier X to report level FL390. I observed no change in the mode C on the next radar update and immediately turned air carrier Y 30 degrees right, he acknowledged. I then turned air carrier X 30 degrees right, he acknowledged and then stated that he would have to slow down the climb. Closest proximity was 3 mi and 1500 ft. Why air carrier X stopped at FL385 is unknown. It is my understanding, as told by another ea-320 pilot, that a standard climb rate from FL350 to FL390 would be 700 FPM. At this rate, air carrier X should have been level within 5 to 6 mins. It took air carrier X over 7 mins before reporting level. It is my opinion that air carrier X was not climbing at an optimum rate. Paragraph 4-89d of the airman's information manual states that a pilot should advise ATC if he cannot climb at an optimum rate.

Related reports:

Google
 

Original NASA ASRS Text

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

Narrative: 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.

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.