Narrative:

I was conducting OJT on the pacific sector. A B737 departed sna and was climbing to assigned altitude of 050; on the channel 1 departure. A PC12 was on vectors for a visual approach to sna. The PC12 was heading 315 at 060. A BE20 was departing sna also climbing to 050. The developmental then issued traffic information to both the B737 and the PC12; both aircraft stating they were searching. A climb clearance was issued to the BE20 to 070; and the read back was blocked on the frequency. The developmental tried to insure the clearance asking 'last call to approach say again.' then the PC12 reported the B737 insight; also the B737 reported the PC12 insight. What had happened was the B737 had taken the BE20's climb clearance to 070 and was climbing through 054 when they responded to a TCAS alert on the PC12. The developmental then instructed the B737 to maintain visual separation and climb to 100. This all happened in seconds and there wasn't anything I; or the developmental; could have done. The similar sounding call signs played a major part to this event [the B737 and BE20 both ended the same]; but in my opinion the real cause was due to the poor quality of radio frequencies that we are using at sct. For the last three to four weeks the workforce has complained about the frequencies; with 5 by 5 being good in actual 1 to 2 of 5 is what were dealing with. I know management and maintenance have been aware of this problem; but something has to be done. Without TCAS this could have been a midair collision. Again something has to be done about the frequencies at sct. Also I explained to the developmental the correct phraseology for use with similar sounding call signs.

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Original NASA ASRS Text

Title: SCT Controller voiced concern regarding several radio frequencies that fail to operate as required; listing a TCAS RA event resulting from the subject communications problem.

Narrative: I was conducting OJT on the Pacific Sector. A B737 departed SNA and was climbing to assigned altitude of 050; on the Channel 1 departure. A PC12 was on vectors for a visual approach to SNA. The PC12 was heading 315 at 060. A BE20 was departing SNA also climbing to 050. The developmental then issued traffic information to both the B737 and the PC12; both aircraft stating they were searching. A climb clearance was issued to the BE20 to 070; and the read back was blocked on the frequency. The developmental tried to insure the clearance asking 'last call to Approach say again.' Then the PC12 reported the B737 insight; also the B737 reported the PC12 insight. What had happened was the B737 had taken the BE20's climb clearance to 070 and was climbing through 054 when they responded to a TCAS alert on the PC12. The developmental then instructed the B737 to maintain visual separation and climb to 100. This all happened in seconds and there wasn't anything I; or the developmental; could have done. The similar sounding call signs played a major part to this event [the B737 and BE20 both ended the same]; but in my opinion the real cause was due to the poor quality of radio frequencies that we are using at SCT. For the last three to four weeks the workforce has complained about the frequencies; with 5 by 5 being good in actual 1 to 2 of 5 is what were dealing with. I know management and maintenance have been aware of this problem; but something has to be done. Without TCAS this could have been a midair collision. Again something has to be done about the frequencies at SCT. Also I explained to the developmental the correct phraseology for use with similar sounding call signs.

Data retrieved from NASA's ASRS site as of July 2013 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.