Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 1
Communication Breakdown
ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance
Human Factors
I was working the final to SNA airport; TUSTIN sector; frequency 121.3. Aircraft X was on a heading 100 at 3;000 MSL on the base. When I reached out to Aircraft X to vector him right turn heading 170 to intercept the localizer Aircraft X was no longer on my frequency. Aircraft X not responding and continuing on heading 100 I reached out to Aircraft X again turning him right heading 270 to join the final. He was no longer on my frequency proceeding towards high MVA of 3;700 followed by 4;400 MVA. I jumped on guard frequency to try to get hold of him; I reached out to SNA Tower whether they had him on frequency and in case they did to give them immediate right turn heading 250 and climbing to 4;000 towards lower terrain and away from proceeding descending traffic from the NE. At the same time all other sectors in the area were trying to reach out to Aircraft X. It is unknown how Aircraft X ended up on SNA Tower frequency and how long he was on their frequency but eventually SNA Tower was instructed to give Aircraft X westbound heading 270 and climb to 5;000 while Aircraft X was in 4;400 MVA at 3;000 still on a heading 100. Aircraft X was also instructed by Tower then to contact approach PACIFIC sector on 128.1.From the Controller point of view I would just recommend extreme vigilance from pilots especially when put on a base. If pilot knows he is flying through the localizer without being told to expect vector to the final across the localizer; he should question that and reach out to someone right away. Especially if he hears the phrase 'clear to land'. That instruction is a Tower responsibility only. If pilot hears that on frequency while thinking he is on approach frequency or any other frequency but Tower; he should follow up and look for solutions immediately.
As the PM (Pilot Monitoring); on downwind at SNA at 3;000 ft.; we were given a right turn to base with an Approach Controller. While on base; now with a [different] Controller; we were expecting a turn to intercept final. When we were not given the turn on a now busy frequency both the Captain and I assumed they had forgotten about us and we asked for a turn with high terrain approaching off of our nose. We were initially given a left turn into the terrain and immediately denied the turn and then we were given a right turn with a climb to 5;000 ft. The radios were very busy and sometimes cutoff; so I spoke clearly and methodically. There was a frequency change given as we leveled off at 5;000 ft. and when we checked in on the frequency we were given 'cleared to land; 20R'. We were approximately 8 miles from the field at 5;000 ft. and confused by the 'clear to land' call; so we requested a turn back to downwind. We were handed off to Approach Control and given vectors back to final and landed uneventfully.Lesson learned; fly the aircraft first which the Captain was doing expertly.  Navigate second; which we did by knowing where we were at and what we were expecting to happen headed toward final and overshooting final.  Communicate by listening closely while talking slowly and methodically on the radio when things get busy.  Always double check your frequency selected on the radio.  Keep your guard volume up loud enough that you can hear clearly; but not a distraction to your primary frequency (mine may have been a bit too low).  After landing and debriefing with the Captain; we assumed there was a handoff issue during a shift change.  There also could have been an inadvertent (unknown) radio change that was off the correct frequency.  We are unsure what actually caused the communication breakdown with ATC; but we were eventually able to get a vector away from the terrain without any alerts along with an altitude change with additional vectors back to final for an uneventful landing.
TRACON Controller and Pilot reported the aircraft went through final approach course heading toward terrain; then switched to tower frequency; resulting in confusion on both sides.  The aircraft was then vectored for another approach.