Narrative:

Light transport at FL390 requested climb to FL430. I advised that unless light transport could be level at FL430 in 3 1/2 mins, it would have to wait until west of stl, due to crossing traffic at FL410 (air carrier). Light transport responded, 'we can do that, we're out of FL390 for FL430 and we'll be level in 3 1/2 mins.' realizing that an actual clearance to climb had not been issued to light transport, the pilot, in my opinion, clearly understood that he had to have his aircraft level at FL430 in the time parameter stated and why. Based on this I acknowledged 'roger, maintain FL430.' by observing the mode C altitude readout light transport over the course of approximately 3 mins, I ascertained that the aircraft's rate of climb appeared to be insufficient to meet the necessary altitude requirement. At this time I told light transport to 'report level at FL430 in 1 min and 15 seconds or less, advise if unable.' light transport responded, 'I'm out of FL420, we've picked up a temperature change.' I reiterated, 'I say again, advise if unable, as quickly as possible.' light transport acknowledged, 'I think we can make it, but it's going to be close, do you want to give me a vector?' I then turned air carrier 20 degrees left, thereby acquiring a small amount of additional time and setting up a better angle for possible evasive action. I went back to light transport and said 'I need you level in 30 seconds, are you going to make it?' light transport advised that he was going to be unable to comply. I turned light transport left heading 170 degrees. I then descended air carrier to FL400. Loss of separation occurred, closest point was 1.9 NM and 1300 ft. Prevention of recurrence can be accomplished by pilot advising controller as soon as possible of possible inability to comply with restriction, controller taking other action immediately upon learning of pilot's doubt.

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Original NASA ASRS Text

Title: LTT CLB THROUGH OCCUPIED ALT HAD LTSS FROM ACR. SYS ERROR.

Narrative: LTT AT FL390 REQUESTED CLB TO FL430. I ADVISED THAT UNLESS LTT COULD BE LEVEL AT FL430 IN 3 1/2 MINS, IT WOULD HAVE TO WAIT UNTIL W OF STL, DUE TO XING TFC AT FL410 (ACR). LTT RESPONDED, 'WE CAN DO THAT, WE'RE OUT OF FL390 FOR FL430 AND WE'LL BE LEVEL IN 3 1/2 MINS.' REALIZING THAT AN ACTUAL CLRNC TO CLB HAD NOT BEEN ISSUED TO LTT, THE PLT, IN MY OPINION, CLRLY UNDERSTOOD THAT HE HAD TO HAVE HIS ACFT LEVEL AT FL430 IN THE TIME PARAMETER STATED AND WHY. BASED ON THIS I ACKNOWLEDGED 'ROGER, MAINTAIN FL430.' BY OBSERVING THE MODE C ALT READOUT LTT OVER THE COURSE OF APPROX 3 MINS, I ASCERTAINED THAT THE ACFT'S RATE OF CLB APPEARED TO BE INSUFFICIENT TO MEET THE NECESSARY ALT REQUIREMENT. AT THIS TIME I TOLD LTT TO 'RPT LEVEL AT FL430 IN 1 MIN AND 15 SECONDS OR LESS, ADVISE IF UNABLE.' LTT RESPONDED, 'I'M OUT OF FL420, WE'VE PICKED UP A TEMP CHANGE.' I REITERATED, 'I SAY AGAIN, ADVISE IF UNABLE, AS QUICKLY AS POSSIBLE.' LTT ACKNOWLEDGED, 'I THINK WE CAN MAKE IT, BUT IT'S GOING TO BE CLOSE, DO YOU WANT TO GIVE ME A VECTOR?' I THEN TURNED ACR 20 DEGS L, THEREBY ACQUIRING A SMALL AMOUNT OF ADDITIONAL TIME AND SETTING UP A BETTER ANGLE FOR POSSIBLE EVASIVE ACTION. I WENT BACK TO LTT AND SAID 'I NEED YOU LEVEL IN 30 SECONDS, ARE YOU GOING TO MAKE IT?' LTT ADVISED THAT HE WAS GOING TO BE UNABLE TO COMPLY. I TURNED LTT L HDG 170 DEGS. I THEN DSNDED ACR TO FL400. LOSS OF SEPARATION OCCURRED, CLOSEST POINT WAS 1.9 NM AND 1300 FT. PREVENTION OF RECURRENCE CAN BE ACCOMPLISHED BY PLT ADVISING CTLR ASAP OF POSSIBLE INABILITY TO COMPLY WITH RESTRICTION, CTLR TAKING OTHER ACTION IMMEDIATELY UPON LEARNING OF PLT'S DOUBT.

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.