B757 TCASII TA RA HAD LTSS WITH COMMUTER ACFT WITH STUCK MIKE. EVASIVE ACTION CLB.

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WHILE ON APCH (LAX ILS 25L) ON APCH FREQ 124.9; RADIO WAS HARD JAMMED WHENEVER CTLR KEYED MIKE. THIS OCCURRED ABOUT 4 MI BEFORE DOWNE AND CONTINUED FOR ABOUT 30 SECONDS OR SO BEFORE WE SWITCHED OVER TO FREQ 128.5. AT THE VERY INSTANT WE REESTABLISHED 2-WAY COM WE GOT A TCASII RA 'CLB' COMMAND PLUS VERBAL INSTRUCTIONS TO IMMEDIATELY CLB TO 4500 FT. WITHIN A VERY FEW SECONDS; CAPT SAW CONFLICTING (A LIGHT TWIN COMMUTER) NBOUND ABOUT 500 FT BELOW US AND XING AT 10 O'CLOCK ABOUT 1000 FT DISTANT. WITHIN ANOTHER SHORT FEW INSTANTS WE HAD PASSED THE TFC AND WITH RWY IN SIGHT WE WERE RECLRED FOR THE APCH AND CLRED TO LAND. AN AGGRESSIVE DSCNT WAS INITIATED AND BY 500 FT AGL WE WERE FULLY STABILIZED IN LNDG CONFIGN AND ON PROFILE. A NORMAL LNDG WAS MADE. SUPPLEMENTAL INFO FROM ACN 296532: THIS IS NOT THE FIRST INSTANCE OF INTENTIONAL JAMMING OR FALSE ATC COMS IN THE LAX AREA. OUR SIT DEMONSTRATES THE SERIOUSNESS OF THIS ACTIVITY AND APPROPRIATE MEASURES SHOULD BE TAKEN TO STOP THE PERPETRATOR. IN THE INTERIM; I RECOMMEND THAT A BACKUP FREQ BE NOTAMED AND TUNED ON THE SECONDARY RADIO FOR BACKUP UNTIL THIS SIT IS STOPPED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: SOCAL TRACON REPRESENTATIVE STATED THEY HAVE HAD NO INCIDENTS BECAUSE OF INTENTIONAL FREQ JAMMING. THERE WAS AN INCIDENT OF A STUCK MIKE BY A COMMUTER ACFT WHICH BLOCKED THE FREQ AND CAUSED LTSS WITH A B757.