Narrative:

Air carrier X was getting chop at FL330 and requested FL370. Pilot was asked how long it would take him to be level FL370. Pilot responded by saying 2 and a half to 3 mins, then corrected himself and said 2 mins. I ran out my 4 min vector lines and showed I had 8-10 mi between the tips of my vector lines. Feeling that the 2 aircraft would be separated in plenty of time I climbed air carrier X to FL370 and asked him to give me his best rate of climb. Conflict alert was activated and I ran out my 2 min vector lines. Still showing 6-8 mi between the tips I asked the pilot if he could be level in 1 and a half mins. Pilot acknowledged with a 'no problem.' advised pilot to report level in 1 min. Pilot said 'roger we're out of FL360 now.' I proceeded to turn both aircraft 20 degrees right. I asked air carrier X to report level now. He came back with, 'we're out of FL360 and a half now.' asked pilot to report level. Pilot advised 'we're at FL367.' pilot then reported level. It took pilot from time he acknowledged the clearance 4 min and 25 seconds to level off at FL370 after stating it would only take him 2 mins. I fully believed the pilot would be able to have his aircraft level in time he stated. My judgement was off by quite a bit. I was trying to help the pilot get to smooth air as quickly as possible and again, the pilot led me to believe his aircraft was capable of something it obviously was not. I should have added a restr to the climb clearance.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR ACFT REQUESTED HIGHER ALT DUE TO TURB IS ISSUED CLB BASED ON BEING LEVEL IN 2 TO 3 MINS. PLT DOESN'T MAKE ALT RESULTING IN LTSS WITH ANOTHER ACFT.

Narrative: ACR X WAS GETTING CHOP AT FL330 AND REQUESTED FL370. PLT WAS ASKED HOW LONG IT WOULD TAKE HIM TO BE LEVEL FL370. PLT RESPONDED BY SAYING 2 AND A HALF TO 3 MINS, THEN CORRECTED HIMSELF AND SAID 2 MINS. I RAN OUT MY 4 MIN VECTOR LINES AND SHOWED I HAD 8-10 MI BTWN THE TIPS OF MY VECTOR LINES. FEELING THAT THE 2 ACFT WOULD BE SEPARATED IN PLENTY OF TIME I CLBED ACR X TO FL370 AND ASKED HIM TO GIVE ME HIS BEST RATE OF CLB. CONFLICT ALERT WAS ACTIVATED AND I RAN OUT MY 2 MIN VECTOR LINES. STILL SHOWING 6-8 MI BTWN THE TIPS I ASKED THE PLT IF HE COULD BE LEVEL IN 1 AND A HALF MINS. PLT ACKNOWLEDGED WITH A 'NO PROB.' ADVISED PLT TO RPT LEVEL IN 1 MIN. PLT SAID 'ROGER WE'RE OUT OF FL360 NOW.' I PROCEEDED TO TURN BOTH ACFT 20 DEGS R. I ASKED ACR X TO RPT LEVEL NOW. HE CAME BACK WITH, 'WE'RE OUT OF FL360 AND A HALF NOW.' ASKED PLT TO RPT LEVEL. PLT ADVISED 'WE'RE AT FL367.' PLT THEN RPTED LEVEL. IT TOOK PLT FROM TIME HE ACKNOWLEDGED THE CLRNC 4 MIN AND 25 SECONDS TO LEVEL OFF AT FL370 AFTER STATING IT WOULD ONLY TAKE HIM 2 MINS. I FULLY BELIEVED THE PLT WOULD BE ABLE TO HAVE HIS ACFT LEVEL IN TIME HE STATED. MY JUDGEMENT WAS OFF BY QUITE A BIT. I WAS TRYING TO HELP THE PLT GET TO SMOOTH AIR AS QUICKLY AS POSSIBLE AND AGAIN, THE PLT LED ME TO BELIEVE HIS ACFT WAS CAPABLE OF SOMETHING IT OBVIOUSLY WAS NOT. I SHOULD HAVE ADDED A RESTR TO THE CLB CLRNC.

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.