A319 flight crew reported the aircraft captured a false localizer on approach to MMMX.

Attributes
ACN	1591845
Time
Date	201811
Local Time Of Day	1201-1800
Place
Locale Reference	MMMX.Airport
State Reference	FO
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	A319
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Person 2
Function	First Officer Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Track / Heading All Types

Narrative:

Executing MMMX ILS DME 2 05R approach; descending mavek inbound on 164 track; and with approach clearance. Aircraft was in nav; managed descent; selected speed (160) with appr armed. Approximately 4 miles before MEX05 the aircraft turned left as if to intercept a localizer course. Pilot flying intervened with heading select in order to return to course. ATC immediately provided vectoring to final just outside plaza at half a dot above GS. Localizer and GS capture were normal final approach was hand-flown with correct FD guidance.the first item on the company arrival ops advisory page is a caution. It states 'false localizer signals have been verified to exist in vicinity of MMMX.'in the majority of final approach scenarios the trigger for arming the approach is hearing 'cleared for the approach'. Doing so in this scenario was inappropriate (too early); and in light of this episode this cautionary note is too vague. More guidance; in reference to the verified false localizer signals; is in order.

Original NASA ASRS Text

Title: A319 flight crew reported the aircraft captured a false localizer on approach to MMMX.

Narrative: Executing MMMX ILS DME 2 05R approach; descending MAVEK inbound on 164 track; and with Approach Clearance. Aircraft was in Nav; Managed Descent; Selected Speed (160) with APPR Armed. Approximately 4 miles before MEX05 the aircraft turned left as if to intercept a LOC course. Pilot Flying intervened with Heading Select in order to return to course. ATC immediately provided vectoring to final just outside PLAZA at half a dot above GS. LOC and GS capture were normal Final approach was hand-flown with correct FD guidance.The first item on the Company Arrival Ops Advisory page is a Caution. It states 'False localizer signals have been verified to exist in vicinity of MMMX.'In the majority of final approach scenarios the trigger for arming the approach is hearing 'Cleared for the approach'. Doing so in this scenario was inappropriate (too early); and in light of this episode this cautionary note is too vague. More guidance; in reference to the verified false localizer signals; is in order.

Data retrieved from NASA's ASRS site 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.