Large Transport; Low Wing; 2 Turbojet Eng
Communication Breakdown; Confusion
Conflict Airborne Conflict; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Chart Or Publication; Procedure
AVSAR 2A arrival into MMMX (same issue applies to all arrivals from the north). Per ATC 'Cleared to descend via AVSAR 2A.' Looking at chart; STAR clearly ends at SMO; not SLM. Altitude at SMO is 12;000 per chart. Passing SLM we noticed traffic below us at 12;000. We were descending from 13;000 over SLM to 12;000.  ATC told us to level off at 13;000; so we climbed back up from about 12;700 to 13;000.ATC appears to be under the impression that the minimum altitude is 13;000 when cleared to descend via. From everything I read and my interpretation; the minimum altitude on the descend via is 12;000 after passing SLM; to SMO.  Someone should clarify this with Mexican ATC.
The reporter had been contacted by his company and informed the minimum altitude on the AVSAR DESCEND VIA clearance is 13;000 FT. The 12;000 FT is an MEA. The reporter considers this to be a formatting issue and if he is confused; no doubt other pilots are also.
I rechecked the arrival and it does end at SMO with an 'at or above' altitude of 12;000 FT. I set 12;000 FT in the altitude window and the First Officer acknowledged the 12;000. After passing SLM; the First Officer started a slow descent out of 13;000 FT for 12;000 FT. Approach Control told us to maintain 13;000 FT due to traffic. At 12;800 FT he climbed back to 13;000 FT. After referencing the FOM and Flight Manual we both agreed 13000 FT should have been set in the altitude window.
A crew cleared to DESCEND VIA the MMMX AVSAR TWO ALPHA crossed SLM at 13;000 FT then began a descent to 12;000 FT; which they believed that to be the SMO crossing altitude; but ATC told them to return to 13;000 FT for traffic. The crew was informed 12;000 FT was the MEA; not segment altitude.