B737-700 captain reported that the localizer and glideslope became unreliable and unusable during tw...

Attributes
ACN	1552254
Time
Date	201806
Local Time Of Day	1201-1800
Place
Locale Reference	MMMX.Airport
State Reference	FO
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Flight Plan	IFR
Component
Aircraft Component	ILS/VOR
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Type 7000
Events
Anomaly	Inflight Event / Encounter Other / Unknown

Narrative:

Arrival into MMMX with thunderstorm and rain shower activity in the area; low visibility required ILS procedure to near minimums. On short final below 1000 feet first officer's flight director commanded left turn away from localizer course. Captain's flight director was providing opposite commands. Approaching minimums localizer guidance went away completely followed shortly by the glideslope guidance on both flight directors. Pilot flying executed missed approach and return for second approach. We experienced identical anomalies on second approach but obtained visual runway references prior to losing localizer and glideslope guidance. ILS navigation checked good on the ground and subsequent approach back into ZZZ confirmed ILS guidance worked normally on both captain and first officer's flight directors. This is a potential safety risk that requires further investigation.

Original NASA ASRS Text

Title: B737-700 Captain reported that the localizer and glideslope became unreliable and unusable during two approaches using the same ILS.

Narrative: Arrival into MMMX with thunderstorm and rain shower activity in the area; low visibility required ILS procedure to near minimums. On short final below 1000 feet First Officer's flight director commanded left turn away from Localizer course. Captain's flight director was providing opposite commands. Approaching minimums Localizer guidance went away completely followed shortly by the glideslope guidance on both flight directors. Pilot Flying executed missed approach and return for second approach. We experienced identical anomalies on second approach but obtained visual runway references prior to losing Localizer and glideslope guidance. ILS NAV checked good on the ground and subsequent approach back into ZZZ confirmed ILS guidance worked normally on both Captain and First Officer's Flight Directors. This is a potential Safety risk that requires further investigation.

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.

B737-700 captain reported that the localizer and glideslope became unreliable and unusable during two approaches using the same ILS.