Narrative:

The tower controller requested a 270 degree heading for a VFR aircraft departing to the west practice area. I approved the request. The cessna called initially departing the airport climbing to maintain VFR conditions at or below 4000 ft MSL. I idented the aircraft and allowed it to continue on an assigned heading of 270 degrees. Approximately 1 min later, the kc-135 departed on a 300 degree heading climbing to 3000 ft MSL. I idented the kc-135 and kept it on the 300 degree heading and climbed it to 4000 ft MSL. Then I instructed the C172 to maintain VFR at or below 3500 ft MSL. I then turned my attention to the other aircraft that I was controling. I observed the kc-135 level at 4000 ft MSL and seeing the cessna was maintaining at or below 3500 ft MSL, I turned the kc-135 to a 170 degree heading for vectors to an ILS approach. I went back to watching the other traffic. I heard the conflict alert go off and looked for the problem. I observed the cessna at 3500 ft MSL and the kc-135 at 4000 ft MSL in the same position. I thought VFR versus IFR, I have 500 ft vertical, I can go back to working the other traffic. I was not aware of the error until the next day when I was called to the office. In hindsight, I should not have allowed the slower aircraft to go ahead of a faster one that would conflict later. Or, had I remembered that with a heavy aircraft I needed 1000 ft, as opposed to 500 ft, I would have either stopped the cessna lower or climbed the kc-135 higher before turning the kc-135 sbound.

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Original NASA ASRS Text

Title: LNK CTLR IS ADVISED LATER THAT INCORRECT HVY JET SEPARATION HAD BEEN APPLIED BTWN A C172 AND A MIL KC35R.

Narrative: THE TWR CTLR REQUESTED A 270 DEG HDG FOR A VFR ACFT DEPARTING TO THE W PRACTICE AREA. I APPROVED THE REQUEST. THE CESSNA CALLED INITIALLY DEPARTING THE ARPT CLBING TO MAINTAIN VFR CONDITIONS AT OR BELOW 4000 FT MSL. I IDENTED THE ACFT AND ALLOWED IT TO CONTINUE ON AN ASSIGNED HDG OF 270 DEGS. APPROX 1 MIN LATER, THE KC-135 DEPARTED ON A 300 DEG HDG CLBING TO 3000 FT MSL. I IDENTED THE KC-135 AND KEPT IT ON THE 300 DEG HDG AND CLBED IT TO 4000 FT MSL. THEN I INSTRUCTED THE C172 TO MAINTAIN VFR AT OR BELOW 3500 FT MSL. I THEN TURNED MY ATTN TO THE OTHER ACFT THAT I WAS CTLING. I OBSERVED THE KC-135 LEVEL AT 4000 FT MSL AND SEEING THE CESSNA WAS MAINTAINING AT OR BELOW 3500 FT MSL, I TURNED THE KC-135 TO A 170 DEG HDG FOR VECTORS TO AN ILS APCH. I WENT BACK TO WATCHING THE OTHER TFC. I HEARD THE CONFLICT ALERT GO OFF AND LOOKED FOR THE PROB. I OBSERVED THE CESSNA AT 3500 FT MSL AND THE KC-135 AT 4000 FT MSL IN THE SAME POS. I THOUGHT VFR VERSUS IFR, I HAVE 500 FT VERT, I CAN GO BACK TO WORKING THE OTHER TFC. I WAS NOT AWARE OF THE ERROR UNTIL THE NEXT DAY WHEN I WAS CALLED TO THE OFFICE. IN HINDSIGHT, I SHOULD NOT HAVE ALLOWED THE SLOWER ACFT TO GO AHEAD OF A FASTER ONE THAT WOULD CONFLICT LATER. OR, HAD I REMEMBERED THAT WITH A HVY ACFT I NEEDED 1000 FT, AS OPPOSED TO 500 FT, I WOULD HAVE EITHER STOPPED THE CESSNA LOWER OR CLBED THE KC-135 HIGHER BEFORE TURNING THE KC-135 SBOUND.

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.