Narrative:

While level at assigned altitude of 9000 ft MSL on a radar vector for the straight in ILS to runway 28 at guadalajara (gdl) mexico (mmgl), gdl approach called 'flight X (garbled) 8000 ft (garbled).' my first officer replied 'understand flight X cleared to 8000 ft?' gdl approach replied 'affirmative and (?) maintain 180 to localizer intercept.' I initiated a descent to 8000 ft and slowed to 180 KIAS. We believed the descent to 8000 ft was appropriate because the GS intercept altitude is 7200 ft. In the vicinity of the gdl 105 degrees/14 NM point we got a GPWS 'too low terrain pull up' warning. I clicked off the autoplt and started a climb at the time we were VMC with all terrain and the airport in sight. At no time was there a conflict with terrain. Passing approximately 8300 ft the GPWS warning stopped. Gdl approach then called and said 'flight X maintain 8500 ft until on the GS, cleared for ILS runway 28.' approach and landing completed without further incident. Gdl approach never questioned our 8000 ft altitude so I assume it was correct. The approach plate shows a 7119 ft hill in the vicinity of the gdl 105 degrees/14 NM. I assume this caused the GPWS warning -- if the database is correct. At no time did we have a map shift, and PNF (first officer) was in raw data to verify our position.

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Original NASA ASRS Text

Title: B757-200 CREW HAD A GPWS TERRAIN WARNING AT MMGL.

Narrative: WHILE LEVEL AT ASSIGNED ALT OF 9000 FT MSL ON A RADAR VECTOR FOR THE STRAIGHT IN ILS TO RWY 28 AT GUADALAJARA (GDL) MEXICO (MMGL), GDL APCH CALLED 'FLT X (GARBLED) 8000 FT (GARBLED).' MY FO REPLIED 'UNDERSTAND FLT X CLRED TO 8000 FT?' GDL APCH REPLIED 'AFFIRMATIVE AND (?) MAINTAIN 180 TO LOC INTERCEPT.' I INITIATED A DSCNT TO 8000 FT AND SLOWED TO 180 KIAS. WE BELIEVED THE DSCNT TO 8000 FT WAS APPROPRIATE BECAUSE THE GS INTERCEPT ALT IS 7200 FT. IN THE VICINITY OF THE GDL 105 DEGS/14 NM POINT WE GOT A GPWS 'TOO LOW TERRAIN PULL UP' WARNING. I CLICKED OFF THE AUTOPLT AND STARTED A CLB AT THE TIME WE WERE VMC WITH ALL TERRAIN AND THE ARPT IN SIGHT. AT NO TIME WAS THERE A CONFLICT WITH TERRAIN. PASSING APPROX 8300 FT THE GPWS WARNING STOPPED. GDL APCH THEN CALLED AND SAID 'FLT X MAINTAIN 8500 FT UNTIL ON THE GS, CLRED FOR ILS RWY 28.' APCH AND LNDG COMPLETED WITHOUT FURTHER INCIDENT. GDL APCH NEVER QUESTIONED OUR 8000 FT ALT SO I ASSUME IT WAS CORRECT. THE APCH PLATE SHOWS A 7119 FT HILL IN THE VICINITY OF THE GDL 105 DEGS/14 NM. I ASSUME THIS CAUSED THE GPWS WARNING -- IF THE DATABASE IS CORRECT. AT NO TIME DID WE HAVE A MAP SHIFT, AND PNF (FO) WAS IN RAW DATA TO VERIFY OUR POS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.