Narrative:

I was working the local control position. A learjet was on final to runway 4L and an AC50 was waiting for departure on runway 36. There was traffic crossing runway 36 so I told the AC50 to taxi into position and hold on runway 36. The learjet asked if he was cleared to land on runway 4L and I said yes. Runway 4L and runway 36 come together at the end but don't cross and can be used for arrs on one; and departures on the other at the same time. I was watching the AC50 and he was crossing runway 36 and going onto runway 4L. I sent the learjet around and got the AC50 back to runway 36 and cleared him for takeoff once the runway was clear. I felt in the back of my mind that I had missed something and the learjet asking about being cleared to land was significant. I told my supervisor about the incident and we listened to the tapes. Instead of telling the AC50 to taxi into position and hold on runway 36; I had said runway 4L. The AC50 read back runway 36 and the learjet asked about the landing clearance on runway 4L at almost the same time. I missed the readback from the AC50. Sometimes when you listen to the tapes you can't believe that you said what you did. Aircraft ask about landing clrncs on final a lot but I had a funny feeling about this time and if I had followed through and made sure with the AC50 about runway 36 I wouldn't have had to send the learjet around. When using runway 36 and runway 4L at the same time I always try to keep a closer eye on the runway end and the aircraft because there is always the possibility of going to the wrong runway because of the runway confign. I said the wrong thing; I didn't catch the readback from the AC50 but at least I saw the situation and sent the learjet around in time to avoid an error. I believe the learjet knew exactly what was going on and would have gone around on his own if I hadn't sent him around. To avoid this situation -- besides the obvious thing of saying what you mean to say -- always listen for a readback and if you don't hear it; ask for it. The pilot read back the instruction but I didn't hear it. I should have asked for a readback since I didn't hear the pilot make the first one.

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Original NASA ASRS Text

Title: LIT CTLR INTENDS TO TAXI AC50 INTO POS ON RWY 36 BUT SAYS RWY 4L. SUBSEQUENTLY THE LEARJET ON FINAL FOR RWY 4L IS INSTRUCTED TO GO AROUND TO AVOID A CONFLICT.

Narrative: I WAS WORKING THE LCL CTL POS. A LEARJET WAS ON FINAL TO RWY 4L AND AN AC50 WAS WAITING FOR DEP ON RWY 36. THERE WAS TFC XING RWY 36 SO I TOLD THE AC50 TO TAXI INTO POS AND HOLD ON RWY 36. THE LEARJET ASKED IF HE WAS CLRED TO LAND ON RWY 4L AND I SAID YES. RWY 4L AND RWY 36 COME TOGETHER AT THE END BUT DON'T CROSS AND CAN BE USED FOR ARRS ON ONE; AND DEPS ON THE OTHER AT THE SAME TIME. I WAS WATCHING THE AC50 AND HE WAS XING RWY 36 AND GOING ONTO RWY 4L. I SENT THE LEARJET AROUND AND GOT THE AC50 BACK TO RWY 36 AND CLRED HIM FOR TKOF ONCE THE RWY WAS CLR. I FELT IN THE BACK OF MY MIND THAT I HAD MISSED SOMETHING AND THE LEARJET ASKING ABOUT BEING CLRED TO LAND WAS SIGNIFICANT. I TOLD MY SUPVR ABOUT THE INCIDENT AND WE LISTENED TO THE TAPES. INSTEAD OF TELLING THE AC50 TO TAXI INTO POS AND HOLD ON RWY 36; I HAD SAID RWY 4L. THE AC50 READ BACK RWY 36 AND THE LEARJET ASKED ABOUT THE LNDG CLRNC ON RWY 4L AT ALMOST THE SAME TIME. I MISSED THE READBACK FROM THE AC50. SOMETIMES WHEN YOU LISTEN TO THE TAPES YOU CAN'T BELIEVE THAT YOU SAID WHAT YOU DID. ACFT ASK ABOUT LNDG CLRNCS ON FINAL A LOT BUT I HAD A FUNNY FEELING ABOUT THIS TIME AND IF I HAD FOLLOWED THROUGH AND MADE SURE WITH THE AC50 ABOUT RWY 36 I WOULDN'T HAVE HAD TO SEND THE LEARJET AROUND. WHEN USING RWY 36 AND RWY 4L AT THE SAME TIME I ALWAYS TRY TO KEEP A CLOSER EYE ON THE RWY END AND THE ACFT BECAUSE THERE IS ALWAYS THE POSSIBILITY OF GOING TO THE WRONG RWY BECAUSE OF THE RWY CONFIGN. I SAID THE WRONG THING; I DIDN'T CATCH THE READBACK FROM THE AC50 BUT AT LEAST I SAW THE SITUATION AND SENT THE LEARJET AROUND IN TIME TO AVOID AN ERROR. I BELIEVE THE LEARJET KNEW EXACTLY WHAT WAS GOING ON AND WOULD HAVE GONE AROUND ON HIS OWN IF I HADN'T SENT HIM AROUND. TO AVOID THIS SITUATION -- BESIDES THE OBVIOUS THING OF SAYING WHAT YOU MEAN TO SAY -- ALWAYS LISTEN FOR A READBACK AND IF YOU DON'T HEAR IT; ASK FOR IT. THE PLT READ BACK THE INSTRUCTION BUT I DIDN'T HEAR IT. I SHOULD HAVE ASKED FOR A READBACK SINCE I DIDN'T HEAR THE PLT MAKE THE FIRST ONE.

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.