Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 26
Situational Awareness; Distraction; Confusion; Communication Breakdown; Troubleshooting
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance
Human Factors; Procedure
Aircraft X was cleared for the ILS Runway 25R from straight in by the DYNR controller.  Aircraft Y was turned base off the downwind by the STAR controller descending to 2200 feet.  Aircraft Y was going to go Runway 24L.  Aircraft Y was not established on final but still on a heading to join the localizer inside of the parallel monitor capture box.  I noticed this; while working PM2 and asked the DYNR controller if he had Aircraft X on frequency; and he did not.  I then asked the PM1 controller if he had Aircraft X on frequency; and he did not.  Subsequently Aircraft X descended out of 3200 feet on the approach and by the time Aircraft X was on PM1 frequency; Aircraft Y was establishing on the localizer.  At this time; Aircraft X was out of 3000 feet descending; next to the Aircraft Y aircraft at 2200 feet.  If the Class Bravo was extended further east  at 2500 feet; the STAR controller would not be inclined to take chances like this.  Further; if there were step downs on both ILS's; like ORD; we could work around this.
SCT Controller reports of a loss of separation he watches happen; tries to make others aware but the aircraft are in a frequency change.