Narrative:

Small transport X was holding north at gck VORTAC at 6000 ft. Atx Y called for his clearance on the gck frequency. The right controller gave atx Y his clearance assigning 5000 ft for his altitude. When atx Y read back his clearance, the right controller thought he said 5000, but from the playback of the tape, he said 9000. Atx Y departed and was observed by the right controller at 5500 ft when the right controller asked about his altitude. Atx Y replied he was out of 5500 ft and was then told to descend and maintain 5000 ft. The error occurred when atx Y climbed above 5000 ft and was within 5 mi of small transport X. I believed this situation happened because the pilot did not listen to his clearance and the right controller did not hear the pilot say 9000. The right controller feels the clarity and quality of the equipment was a causal factor in this situation.

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Original NASA ASRS Text

Title: ATX Y READ BACK WRONG ALT CLB THROUGH OCCUPIED ALT HAD LTSS FROM SMT X. SYS ERROR.

Narrative: SMT X WAS HOLDING N AT GCK VORTAC AT 6000 FT. ATX Y CALLED FOR HIS CLRNC ON THE GCK FREQ. THE R CTLR GAVE ATX Y HIS CLRNC ASSIGNING 5000 FT FOR HIS ALT. WHEN ATX Y READ BACK HIS CLRNC, THE R CTLR THOUGHT HE SAID 5000, BUT FROM THE PLAYBACK OF THE TAPE, HE SAID 9000. ATX Y DEPARTED AND WAS OBSERVED BY THE R CTLR AT 5500 FT WHEN THE R CTLR ASKED ABOUT HIS ALT. ATX Y REPLIED HE WAS OUT OF 5500 FT AND WAS THEN TOLD TO DSND AND MAINTAIN 5000 FT. THE ERROR OCCURRED WHEN ATX Y CLBED ABOVE 5000 FT AND WAS WITHIN 5 MI OF SMT X. I BELIEVED THIS SITUATION HAPPENED BECAUSE THE PLT DID NOT LISTEN TO HIS CLRNC AND THE R CTLR DID NOT HEAR THE PLT SAY 9000. THE R CTLR FEELS THE CLARITY AND QUALITY OF THE EQUIP WAS A CAUSAL FACTOR IN THIS SITUATION.

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.