Narrative:

Aircraft a (small transport) departed tpa for tmb requesting 17,000. Aircraft B (small transport) northbound from fmy pie tlh at 14,000. Aircraft a came on the frequency and was cleared to 14,000 and issued traffic 11 O'clock 10 mi northbound at 14,000. Aircraft a answered with last 2 letters of his call sign only. Aircraft B was issued traffic 12 O'clock 5 mi southbound, am small transport climbing to 13,000'. Aircraft B said roger. At XXXX separation was lost. The controller saw the traffic but cleared aircraft a to 14,000' instead of 13,000', which he meant to do. The reason for this report: if it was mandatory for pilots to read back a clearance for an altitude, maybe this system error would have been prevented.

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Original NASA ASRS Text

Title: ACFT A AND ACFT B OPPOSITE DIRECTION IFR AT THE SAME ALT. LESS THAN STANDARD SEPARATION. SYSTEM ERROR.

Narrative: ACFT A (SMT) DEPARTED TPA FOR TMB REQUESTING 17,000. ACFT B (SMT) NBOUND FROM FMY PIE TLH AT 14,000. ACFT A CAME ON THE FREQ AND WAS CLRED TO 14,000 AND ISSUED TFC 11 O'CLOCK 10 MI NBOUND AT 14,000. ACFT A ANSWERED WITH LAST 2 LETTERS OF HIS CALL SIGN ONLY. ACFT B WAS ISSUED TFC 12 O'CLOCK 5 MI SBND, AM SMT CLIMBING TO 13,000'. ACFT B SAID ROGER. AT XXXX SEPARATION WAS LOST. THE CTLR SAW THE TFC BUT CLRED ACFT A TO 14,000' INSTEAD OF 13,000', WHICH HE MEANT TO DO. THE REASON FOR THIS REPORT: IF IT WAS MANDATORY FOR PLTS TO READ BACK A CLRNC FOR AN ALT, MAYBE THIS SYSTEM ERROR WOULD HAVE BEEN PREVENTED.

Data retrieved from NASA's ASRS site as of August 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.