Narrative:

I was working combined position local control-ground control. Small aircraft X reported left downwind for runway 17, then changed his report to say he was on a right downwind. An small aircraft called for takeoff to remain in pattern. Small aircraft was cleared for takeoff. Small aircraft X was cleared to land. Small aircraft Y called for takeoff. Small aircraft Y was advised to hold short because of small aircraft just taxiing into position. After small aircraft started his takeoff roll, small aircraft Y was instructed to taxi into position to hold. Small aircraft X was on right base at this time. I was waiting for 3000' sep to depart small aircraft Y, when the air conditioner compressor lights came on and air conditioner located on tip of cabin attendant sounded abnormal. I went over to shut air conditioner off. I returned to local control position and observed small aircraft X on short final landing after small aircraft X landed. Small aircraft Y called and wanted to know what was going on and why did small aircraft X land over the top of him, holding in position. I was convinced that I had cleared small aircraft Y for takeoff until I listened to the tape and there was no clearance on the tape. The air conditioner failure broke my concentration and I returned to the position west/O thinking about small aircraft Y. Small aircraft Y is a grey aircraft and sunset was 10 mins earlier. I never saw small aircraft Y holding in position because my mind already had him departing and it was between twilight and dark. The tower cabin attendant air conditioner had been out for 3 hours previously with outside air temperature 94 degrees. 1 controller had departed earlier on sick leave because of the high temperature in cabin attendant. I feel the failure of the air conditioner compressors was a contributing factor in that it definitely broke my concentration on local control position.

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Original NASA ASRS Text

Title: SMA X LANDED OVER SMA Y HOLDING IN POSITION ON RWY. LESS THAN STANDARD SEPARATION. SYSTEM ERROR.

Narrative: I WAS WORKING COMBINED POS LC-GC. SMA X RPTED L DOWNWIND FOR RWY 17, THEN CHANGED HIS RPT TO SAY HE WAS ON A R DOWNWIND. AN SMA CALLED FOR TKOF TO REMAIN IN PATTERN. SMA WAS CLRED FOR TKOF. SMA X WAS CLRED TO LAND. SMA Y CALLED FOR TKOF. SMA Y WAS ADVISED TO HOLD SHORT BECAUSE OF SMA JUST TAXIING INTO POS. AFTER SMA STARTED HIS TKOF ROLL, SMA Y WAS INSTRUCTED TO TAXI INTO POS TO HOLD. SMA X WAS ON R BASE AT THIS TIME. I WAS WAITING FOR 3000' SEP TO DEPART SMA Y, WHEN THE AIR CONDITIONER COMPRESSOR LIGHTS CAME ON AND AIR CONDITIONER LOCATED ON TIP OF CAB SOUNDED ABNORMAL. I WENT OVER TO SHUT AIR CONDITIONER OFF. I RETURNED TO LCL CTL POS AND OBSERVED SMA X ON SHORT FINAL LNDG AFTER SMA X LANDED. SMA Y CALLED AND WANTED TO KNOW WHAT WAS GOING ON AND WHY DID SMA X LAND OVER THE TOP OF HIM, HOLDING IN POS. I WAS CONVINCED THAT I HAD CLRED SMA Y FOR TKOF UNTIL I LISTENED TO THE TAPE AND THERE WAS NO CLRNC ON THE TAPE. THE AIR CONDITIONER FAILURE BROKE MY CONCENTRATION AND I RETURNED TO THE POS W/O THINKING ABOUT SMA Y. SMA Y IS A GREY ACFT AND SUNSET WAS 10 MINS EARLIER. I NEVER SAW SMA Y HOLDING IN POS BECAUSE MY MIND ALREADY HAD HIM DEPARTING AND IT WAS BTWN TWILIGHT AND DARK. THE TWR CAB AIR CONDITIONER HAD BEEN OUT FOR 3 HRS PREVIOUSLY WITH OUTSIDE AIR TEMP 94 DEGS. 1 CTLR HAD DEPARTED EARLIER ON SICK LEAVE BECAUSE OF THE HIGH TEMP IN CAB. I FEEL THE FAILURE OF THE AIR CONDITIONER COMPRESSORS WAS A CONTRIBUTING FACTOR IN THAT IT DEFINITELY BROKE MY CONCENTRATION ON LC POS.

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.