Narrative:

Air carrier X departed denver and checked on my frequency climbing to FL260; requesting FL350. I cleared the aircraft to climb to FL330; the top of my stratum and entered an interim altitude of FL330 into the data block. As far as I know; he read back the correct altitude. I noticed a limited data block at FL340 (air carrier Y; westbound for slc) converging with air carrier X and told the air carrier X to expect higher in about 4 minutes clearing traffic and 'shipped' him to sector 30. The developmental on sector 30 acknowledged the check-on by air carrier X and as far as I know; did not issue a climb clearance to him. A few minutes passed and I hear the instructor say; 'uh-oh; that's not good'; and immediately issued turns to both aircraft and an immediate descent clearance to FL330 for air carrier X. The instructor did this before conflict alert activated and kept the aircraft separated. The questions I have are; did I miss clear the air carrier X to FL340 and not realize it? Did I clear him to FL330 and miss the bad read back? Was the read back good but the pilot enter FL340 into his FMS? What altitude did he say he was climbing to when he checked on with sector 30? Recommendation; I should have issue merging target procedures to air carrier X with his FL340 converging traffic so as to clue him into his actual assigned altitude. I didn't do it initially because they were still about 40 miles apart when I shipped him to sector 30; but I should have anyway just to reinforce the clearance. Data link would be a nice tool.

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Original NASA ASRS Text

Title: ZDV controller described near separation loss when receiving controller had too immediately issue turns and altitude changes to prevent a conflict; the reporter questioning clearance read back accuracy.

Narrative: Air Carrier X departed Denver and checked on my frequency climbing to FL260; requesting FL350. I cleared the aircraft to climb to FL330; the top of my stratum and entered an interim altitude of FL330 into the data block. As far as I know; he read back the correct altitude. I noticed a limited data block at FL340 (Air Carrier Y; westbound for SLC) converging with Air Carrier X and told the Air Carrier X to expect higher in about 4 minutes clearing traffic and 'shipped' him to Sector 30. The developmental on Sector 30 acknowledged the check-on by Air Carrier X and as far as I know; did not issue a climb clearance to him. A few minutes passed and I hear the instructor say; 'Uh-oh; that's not good'; and immediately issued turns to both aircraft and an immediate descent clearance to FL330 for Air Carrier X. The instructor did this before conflict alert activated and kept the aircraft separated. The questions I have are; did I miss clear the Air Carrier X to FL340 and not realize it? Did I clear him to FL330 and miss the bad read back? Was the read back good but the pilot enter FL340 into his FMS? What altitude did he say he was climbing to when he checked on with Sector 30? Recommendation; I should have issue merging target procedures to Air Carrier X with his FL340 converging traffic so as to clue him into his actual assigned altitude. I didn't do it initially because they were still about 40 miles apart when I shipped him to Sector 30; but I should have anyway just to reinforce the clearance. Data link would be a nice tool.

Data retrieved from NASA's ASRS site as of April 2012 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.