Narrative:

C550 climbing out of henderson; nv; was leaving FL240 for FL330. B737 climbing out of las was within 5 mi so I used altitude leaving and climbed B737 to FL240. B737 read back FL340. Our frequencys are notoriously bad and have been reported so for months. I thought he said 240 and B737 climbed through FL240 to FL250. Once noticing this I stopped his climb to FL250. Something should be done with these horrible frequencys!

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Original NASA ASRS Text

Title: ZLA CTLR EXPERIENCED OPERROR AT APPROX FL250 WHEN INCORRECT READBACK WAS NOT HEARD AND ACFT INITIATED CLIMB TO CONFLICTING ALT.

Narrative: C550 CLBING OUT OF HENDERSON; NV; WAS LEAVING FL240 FOR FL330. B737 CLBING OUT OF LAS WAS WITHIN 5 MI SO I USED ALT LEAVING AND CLBED B737 TO FL240. B737 READ BACK FL340. OUR FREQS ARE NOTORIOUSLY BAD AND HAVE BEEN RPTED SO FOR MONTHS. I THOUGHT HE SAID 240 AND B737 CLBED THROUGH FL240 TO FL250. ONCE NOTICING THIS I STOPPED HIS CLB TO FL250. SOMETHING SHOULD BE DONE WITH THESE HORRIBLE FREQS!

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.