B737-800 CREW HAD AN ENHANCED GPWS 'PULL UP TERRAIN' WARNING WHILE BEING VECTORED FOR THE ILS RWY 28 AT MMGL.

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ON VECTOR; APPROX 15 NM NE GDL; TO INTERCEPT LOC 28 ON 260 HDG. PRIOR TO INTERCEPTING LOC RECEIVED GPWS 'PULL-UP' ONCE. WX WAS SCATTERED LAYER AT AND SLIGHTLY BELOW 8000 FT MSL. PER COMPANY PROCEDURE WE CLBED (1000 FT) TO VFR VISUALLY CLEAR OF TERRAIN AND INFORMED GDL ATC OF OUR ACTION. NO OTHER INDICATIONS OF CLOSING TERRAIN WERE NOTED (IE RADIO ALT). WE WERE RE-VECTORED FOR AN ILS TO VISUAL RWY 28 WITH UNEVENTFUL NORMAL LNDG. WE DEBRIEFED THE EVENT AFTER LNDG AND DECIDED TO VISIT GDL TWR/APCH. WE REVIEWED THE APCH PLATE AND RELATED OBSTACLES RELATIVE TO OUR RADAR AND FLIGHT PATH WITH THE APCH CTLR. WE FELT THAT THE VECTOR AT 8000 FT MSL MIGHT HAVE BROUGHT US TOO CLOSE TO AN OBSTRUCTION AT 7119 FT MSL JUST INSIDE 14 DME ON FINAL. THE CTLR STATED HE HAD VECTORED US ABOUT 3NM N OF THAT POINT AND AT THE TIME WE BEGAN OUR CLB WE WERE OVER 6100 FT MSL TERRAIN. NO CONFLICTS OCCURRED AND ATC HAD NO PROBLEM WITH OUR TERRAIN AVOIDANCE MANEUVER. WE HAVE REFERRED THE MATTER INTERNALLY TO OUR ATC SPECIALISTS AND EQUIP SPECIALISTS TO REVIEW THE CAPABILITIES AND LIMITATIONS OF OUR GPWS RELATIVE TO GDL APCH PROCS. WE DID NOTE THE FOLLOWING DAY WE RECEIVED VECTORS FOR THE ILS OVER APPROX THE SAME AREA. AT 13.1 DME AND 090 BEARING WE WERE GIVEN 8000 FT. THE AREA CHART MVA SHOWS 9000 FT. I HAVE SUGGESTED THE MVA IN THE AREA OF 14 MI FINAL TO RWY 28 BE 8300 TO ALLOW FOR POSSIBLE GPWS LIMITATIONS AND CONFORM TO MIN ALT ON APCH PLATE STEP DOWN. SUPPLEMENTAL INFO FROM ACN 593749: WE FELT THAT THE 8000 FT MSL VECTOR MAY HAVE BROUGHT US TOO CLOSE TO A 7119 MSL OBSTRUCTION JUST INSIDE 14 DME ON FINAL. THE CTLR STATED HE HAD VECTORED US ABOUT 3 NM N OF THAT POINT AND AT THE TIME WE BEGAN OUR CLB. WE HAVE REFERRED THE MATTER TO OUR ATC SPECIALIST. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CREW RPTED THE INCIDENT TO THEIR ACR SAFETY DEP. A COMPLETE READOUT OF FLT RECORDER WAS PRINTED. TRIGGERING OCCURRED AT N 20.43.59; W 103.08.47; ON A HDG OF 260; AT A RADIO ALT OF 1426 FT AGL; AT AN AIRSPEED OF 179.4 KTS. THIS CAPT FLIES INTO MMGL FREQUENTLY. THIS WAS THE FIRST TIME HE GOT A EGPWS WARNING. HE SAID THERE IS ALWAYS A PROBLEM GETTING DOWN AT THIS ARPT. HE WOULD LIKE TO SEE THE MIN RADAR VECTORING ALT BE MATCHED TO THAT DEPICTED ON THE APCH PLATE; OF 8300 FT. HE WOULD ALSO LIKE THE EGPWS TRIGGERING ALT BE LOWERED SLIGHTLY.