MD80 CREW HAD A GPWS 'TERRAIN TERRAIN' WARNING WHILE ON VECTORS AT MMMX.

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EGPWS ESCAPE ALT DEV MMEX. NIGHT IMC TSTMS AT MMMX CLEARED DIRECT FROM PCA TO SMO ON ROLLOUT DIRECT LEVEL 3 TSTMS IN LINE DIRECTLY TO SMO AND OVER SMO. REQUESTED OFFSET 2-3 MILES RIGHT OF CRS FOR TSTM AVOIDANCE--GRANTED. APCH URGED LEFT TURN SMO ASAP-UNABLE TSTMS. I HAD HOPED FOR MANEUVERING AIRSPACE ON THE SOUTH SIDE OF SMO--UNABLE DIRECT SMO-TERRAIN ON N AND E SIDE OF SMO. ABEAM SMO ATC DIRECTED LEFT TURN HEADING 140 TO INTERCEPT SMO 160 PER APCH. TURNED LEFT ON LEADING EDGE OF STORM-MODERATE CHOP LTG CTC AUTOPLT AND ATS TRIPPED OFF--DECIDED THAT WE COULDN'T DSND PER APCH ON 160 RADIAL EVEN THOUGH WE WERE CLRED BY ATC TO DSND BECAUSE I FELT WE NEEDED CRS GUIDANCE TO ASSURE 12000 FOOT MSA CLRNC. BY THEN WE WERE SOUTH OF SMO STILL AT 11000 FT AND I ANTICIPATED THAT EVEN IF WE COULD INTERCEPT LOC; WE'D BE TOO HIGH IMC FOR SAFE DSCNT. BUT WE WERE NOT CLRED FOR APCH SO NO MISSED APCH WAS AVAILABLE--FREQ CONGESTION--UNABLE TO CALL ATC. I TOLD FO TELL THEM WE'RE GOING MISSED-WITHIN SECOND WE GOT EGPWS 'TERRAIN-PULL UP' WARNING. EXECUTED RED BOX RADIO ALTIMETER CAME ALIVE AND PASSED THROUGH 1000 FT; IAS DOWN TO 160 KTS WITH FLAPS 11. TOLD FO TO NOTIFY ATC THAT WE WERE CLBING TO MSA DIRECT MEX VOR TO HOLD. BOTH ENGS AT FIREWALL FOR APPROX 30 SECS. ATC KEPT ASKING IF WE COULD ACCEPT HEADINGS S FOR ANOTHER APCH--AT THAT POINT OUR SITUATIONAL AWARENESS WAS OBVIOUSLY COMPROMISED SO I REFUSED ALL OFFERED HDGS DSCNTS AND REITERATED THAT WE WOULD LEVEL AT MSA; HOLD AT VOR AND REGROUP. ATC ASKED US TOLD MOVE S TO HOLD; WE AGREED; BUT THEY CLRED US TO 12000 FT;. THEY CLRED US TO HOLD MEX180 TEN MI LEGS AT 12000 FT BUT MSA WAS 14000 IN THAT SECTOR; REFUSED HOLD AND AFTER LEVEL FLT AT MSA WITH AUTOPLT AND ATS BACK WE DETERMINED WITH 14.7 LEGS FUEL WE COULD ACCEPT ONE SET OF VECTORS ON S SIDE OF SMO TSTM WITH CLRNC ON REQ TO ACA IF UNABLE. GOT VECTORS ON S SIDE; SKIRTED TSTM AND LANDED. CONTRIBUTING FACTORS TO THIS TERRAIN CLOSURE INCLUDE FREQ CONGESTION AND INABILITY TO GET MANEUVERING AIRSPACE. FURTHER; WITH MOST ACFT ON FREQ SPEAKING SPANISH; WE WERE UNABLE TO DETERMINE WHO WAS WHERE AND HOW OTHER ACFT WERE FINDING THEIR WAY THROUGH THE WX. ALSO; OLD-STYLE FMS HAD ME PUSHING BUTTONS ON EGPWS WX LIKE A MADMAN TRYING TO MONITOR BOTH WHILE WE USED THE TAIL OF THE BEARING POINTER FOR BEARING DME TO APPROX OUR POSITION REGARDING TERRAIN. MOUNTING RING--FSA/S-FREQ CONGESTION AND LANGUAGE HAVE A DEGRADING EFFECT ON SA AND ESCAPE OPTIONS. IF I HAD IT TO DO OVER I WOULD NOT HAVE ASSUMED ENRTE PCA-SMO THAT ATC WOULD ACCEPT MY NEED TO MANEUVER ON THE S SIDE OF SMO; AND I WOULD HAVE DECLARED AN EMER UPON ESCAPE MANEUVER TO ACCOUNT FOR OUR INSISTENCE ON A CLB TO MSA. NIGHT; IMC; TSTMS; MOUNTAINS AND LANGUAGE/CONGESTION FACTORS AT MMMX ARE A SERIOUS SAFETY LIABILITY. I AM GRATEFUL FOR EGPWS AND BELIEVE IT SHOULD BE MANDATORY FOR GDL AND MEX AND URGE THE SOONEST RETROFIT FOR MD80 GFMS NAV DISPLAYS FOR OBVIOUS REASONS. SUPPLEMENTAL INFO FROM ACN 565113: IMC ARR IN MEX TERMINAL AREA WITH TSTMS (TOWERING TSTMS) VICINITY OF SMO VOR. ATC DIRECTED EXPECT ILS DME-2 RWY 05R. ATC VECTORED FLT NW; W; SW OF SMO VOR AT 12000 FT AND 11000 FT IN ATTEMPT TO AVOID TCU AND SETUP INTERCEPT OF SMO 160R FOR APCH. APP DIRECTED DSCNT TO 9-700 FT IN EFFORT TO PICK UP ARR PROFILE. ONCE LEVEL AT 9700 FT CA ELECTED TO INITIATE TURN TOWARDS MEX VOR TO AVOID HIGH TERRAIN TO SW. EGPWS ALERT SOUNDED AND TERRAIN AVOIDANCE RED BOX PROCS WERE EXECUTED WITH A CLB TO MSA OF 12000 FT. CREW REQUESTED TO HOLD AT MEX VOR AND WAS DIRECTED TO HOLD S ON 180R; 10 DME LEGS AT 12000 FT. FOLLOW ON CTLR DIRECTED CLB TO 14000 FT PRIOR TO ENTERING A SECTOR WITH MIN RADAR VECTOR ALT OF 14000 FT. VECTORS AND DSCNT WERE COORDINATED FOR A RIGHT BASE INTERCEPT OF RWY 05R LOC FOR APP AND LNDG AT MMMX.