Date: 201508
Local time of day: 0601-1200
Location: MMSD.Airport, FO
Flight conditions: VMC
Light: Daylight
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
ATC / advisory: TRACON MMSD
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Distraction; Situational Awareness
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: En route to Cabo; was cleared ENEKO then our filed route direct to Cabo. The First Officer was flying and I was monitoring. On descent I received call from another company flight going to MMGL and said they had a mechanical and couldn't raise company and asked if I could contact them. I sent an ACARS to the company as we continued in. After switching to Cabo Approach was cleared to 5100 ft. We were still proceeding direct Cabo VOR. Then the Approach Controller cleared us for the VOR 2 runway 16 approach. I then received an ACARS from the company requesting [we] tell the other flight to turn back to ZZZ. I tried to call them but no answer. At that point Approach Control asked why we depended below 5100 ft. I ask the FO and he said they had cleared us for the approach and the altitude was 3600.I checked and he was right and told Approach that he had cleared us for the VOR 2 approach and we had the airport in sight and could take a visual. He responded he did not clear us for the visual and we [had] descended below minimum vectoring altitude. I told him we had misunderstood what he wanted and at the time he cleared us to 2400 ft and then cleared us for the visual approach. After landing I discussed what happened with the FO. He said he had proceeded direct to the 18 mile IF on the VOR 2 approach while I was off the radio. I was distracted and realized we were not on an established segment of the approach and should have not accepted the approach as cleared. They usually clear us to MARUK and then the approach but at the time we were still going direct to Cabo. We were only a few degrees off the inbound and visual so the FO thought we could just intercept the inbound course and descend to that crossing altitude.The main part on my behalf was the distraction of trying to help the other flight communicate with company so I was out of the loop. The FO should have said we were not on a part on the approach and I should have seen this too and never accepted it as cleared. If I had not been distracted I should have seen this and not accepted the approach as cleared.As at all times I should have not let the company call distract me; and as at all times in in foreign country I should have verified the clearance he gave us.




Synopsis: A320 Captain reported the flying First Officer descended below cleared altitude on approach to MMSD after misunderstanding an ATC clearance.