Narrative:

While working the st johns sector at ZJX; I issued a clearance to air carrier X to 'fly heading 330 vector for your climb.' the pilot responded 'up to 330 assigned.' instead of taking that as a vector clearance; the air carrier took that as a climb clearance. Air carrier X was then xferred communications to the keystone sector and never checked on; instead just sitting on the frequency -- all the while in a climb to FL330 in the same direction as the B737 in VMC. Keystone sector attempted to have the air carrier stop his climb out of FL235; however; by that time the air carrier aircraft had already passed through FL240. The closest these 2 planes got within each other was 500 ft and 2.3 mi. I understand as the controller that issued the vector to the aircraft; I should have caught the bad readback with un-prescribed phraseology. I do feel that the air carrier pilot should be given a major part of the blame here as well: 1) he clearly missed a clear understandable clearance for the vector. 2) he used no prescribed phraseology in his readback of the clearance. 3) he did not check on to the relieving sector. 4) and the most important reason -- he climbed in VMC and yet failed to see a B737 at 500 ft and 2 1/2 mi.

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Original NASA ASRS Text

Title: ZJX CTLR EXPERIENCED OPERROR AT FL250 AS FLT CREW MISTAKES HDG FOR ALT ASSIGNMENT AND CTLR FAILS TO HEAR AND RESPOND TO INCORRECT READBACK.

Narrative: WHILE WORKING THE ST JOHNS SECTOR AT ZJX; I ISSUED A CLRNC TO ACR X TO 'FLY HDG 330 VECTOR FOR YOUR CLB.' THE PLT RESPONDED 'UP TO 330 ASSIGNED.' INSTEAD OF TAKING THAT AS A VECTOR CLRNC; THE ACR TOOK THAT AS A CLB CLRNC. ACR X WAS THEN XFERRED COMS TO THE KEYSTONE SECTOR AND NEVER CHKED ON; INSTEAD JUST SITTING ON THE FREQ -- ALL THE WHILE IN A CLB TO FL330 IN THE SAME DIRECTION AS THE B737 IN VMC. KEYSTONE SECTOR ATTEMPTED TO HAVE THE ACR STOP HIS CLB OUT OF FL235; HOWEVER; BY THAT TIME THE ACR ACFT HAD ALREADY PASSED THROUGH FL240. THE CLOSEST THESE 2 PLANES GOT WITHIN EACH OTHER WAS 500 FT AND 2.3 MI. I UNDERSTAND AS THE CTLR THAT ISSUED THE VECTOR TO THE ACFT; I SHOULD HAVE CAUGHT THE BAD READBACK WITH UN-PRESCRIBED PHRASEOLOGY. I DO FEEL THAT THE ACR PLT SHOULD BE GIVEN A MAJOR PART OF THE BLAME HERE AS WELL: 1) HE CLRLY MISSED A CLR UNDERSTANDABLE CLRNC FOR THE VECTOR. 2) HE USED NO PRESCRIBED PHRASEOLOGY IN HIS READBACK OF THE CLRNC. 3) HE DID NOT CHK ON TO THE RELIEVING SECTOR. 4) AND THE MOST IMPORTANT REASON -- HE CLBED IN VMC AND YET FAILED TO SEE A B737 AT 500 FT AND 2 1/2 MI.

Data retrieved from NASA's ASRS site as of January 2009 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.