B747 Undifferentiated or Other Model
Air Traffic Control Developmental
Communication Breakdown; Situational Awareness
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
ATC Equipment / Nav Facility / Buildings; Airspace Structure; Human Factors; Procedure
I was working Ontario arrivals sector. It was east traffic. Flows are different than normal west configuration. I was getting arrivals from Center on frequency 127.0. I should have switched aircraft over to 125.5 as they transitioned my airspace. I had a few arrivals go in without the frequency switch so I felt that it was okay leaving the aircraft on 127.0. Aircraft X was given a turn to base heading 360 to maintain 3000 feet. The Pilot read it back and made the turn. About 30 seconds later I gave Aircraft X a turn to final and the approach clearance. Aircraft X does not respond. I tried multiple times but could not get through. I was able to use an aircraft to aircraft relay to get Aircraft X on a turn away from terrain and to have them change to my frequency 125.5. When I was able to reach Aircraft X I issued a low altitude alert and turned them south to resequence. I need to make sure to switch aircraft as they are transitioning from sector to sector even when I am working combined. I will work on having a better knowledge of gaps in the frequencies and where the problem spots are. I will also review east traffic procedures so that I am more familiar with them when we do go east.
ATC Controller reported allowing an aircraft to remain on the previous (combined) frequency; then lost communications as the aircraft flew below the Minimum Vectoring Altitude.