A319
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Total 8
Situational Awareness
Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Provided Assistance; Flight Crew Became Reoriented
Human Factors; Procedure
On downwind abeam KSAN at 5000'; given a base turn to final just outside of SAYAE; extended off of SAYAE and was in the turn to intercept final; cleared to 3800 until established on final. Armed app; descended to the crossing alt 3200 for SAYAE; told by ATC that we had an altitude deviation at 3400; due to the MVA altitude for that airspace. I extended off of SAYAE; maybe if I had extended off of OKAIN of VYDDA my SA would have been better as to where 3800 would have put me in relation to final; but the controller turned me in to intercept and as far as I could see; SAYAE was the logical point to extend from. Had we not started our descent when we did; very likely we would have crossed SAYAE at 3800; 600' higher than the charted altitude and would have been very difficult to have been stable at 1000 on an already aggressive approach; (3.5 degree final.)On downwind I should have asked what approach we were being set up for; I should have just said I wanted vectors to LYNDI for the full RNAV approach to 27. I wasn't given a 'cleared for the app' ; just a turn to and maintain 3800 till established; which had us way high for that part of the approach; there's very little distance between OKAIN and SAYAE (1.9) and VYDDA and OKAIN (2.0). When given vectors close in to final; and you're high; descending; very challenging to see exactly which point to extend off; so I took the point that appears to me that's in front of us. Even if it was just a visual. [Also] I don't recall being cleared for a visual; so I can't honestly tell what we were cleared for; we should have waited to engage the APP button till established on final; at least in this scenario.
A319 Captain reported momentary loss of situational awareness resulting in excursion from assigned altitude when assigned base turn to final until established on final.