ATC approach controller reported miscommunication between aircraft resulting in aircraft descending ...

Narrative:

I had 2 aircraft on frequency landing at ZZZ. I had aircraft Y on a vector for a visual at 5;000; and aircraft X on a vector for an ASR (approach surveillance radar) at 10;000. I issued a descent to 4;000 and a frequency change to ZZZ to aircraft Y. Aircraft X read back these instructions. I caught a correct read back of the instructions but did not catch the incorrect call sign. Aircraft X was in an 8;700 MVA (minimum vectoring altitude). I noticed the aircraft descending through 8;900; reached out on frequency then issued a low altitude alert when I observed him leaving the MVA altitude. Then on both UHF and VHF guard frequencies. Reached out to the previous sector to see if they came back and also to verify they were in fact IFR and not miss tagged. Center verified they were IFR and that they didn't have them. Aircraft X returns to frequency; ZZZ later said they sent him back when he came over to them. Once on frequency I again issued low altitude alert; verified he did have terrain in sight; and climbed them back up. At this point I did have the evom map up. We sorted out what had happened. I eventually descended him back in for the approach; switched to ZZZ; aircraft landed safely. The pilot misheard who the instructions were for and I missed the call sign on read back.

Original NASA ASRS Text

Title: ATC Approach Controller reported miscommunication between aircraft resulting in aircraft descending below the MVA.

Narrative: I had 2 aircraft on frequency landing at ZZZ. I had Aircraft Y on a vector for a visual at 5;000; and Aircraft X on a vector for an ASR (Approach Surveillance Radar) at 10;000. I issued a descent to 4;000 and a frequency change to ZZZ to Aircraft Y. Aircraft X read back these instructions. I caught a correct read back of the instructions but did not catch the incorrect call sign. Aircraft X was in an 8;700 MVA (Minimum Vectoring Altitude). I noticed the aircraft descending through 8;900; reached out on frequency then issued a low altitude alert when I observed him leaving the MVA altitude. Then on both UHF and VHF guard frequencies. Reached out to the previous sector to see if they came back and also to verify they were in fact IFR and not miss tagged. Center verified they were IFR and that they didn't have them. Aircraft X returns to frequency; ZZZ later said they sent him back when he came over to them. Once on frequency I again issued low altitude alert; verified he did have terrain in sight; and climbed them back up. At this point I did have the EVOM map up. We sorted out what had happened. I eventually descended him back in for the approach; switched to ZZZ; aircraft landed safely. The pilot misheard who the instructions were for and I missed the call sign on read back.

Data retrieved from NASA's ASRS site 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.

Attributes
ACN	1757992
Time
Date	202008
Local Time Of Day	0001-0600
Place
Locale Reference	SCT.TRACON
State Reference	CA
Aircraft 1
Make Model Name	Military
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Military
Operating Under FAR Part	Part 91
Flight Phase	Descent
Flight Plan	IFR
Person 1
Function	Approach
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT

ATC approach controller reported miscommunication between aircraft resulting in aircraft descending below the MVA.