Medium Large Transport
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Clearance; Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem
Aircraft; Environment - Non Weather Related
This event has happened to me on my last 3 trips to MMMX in almost exactly the same location while executing the ILS DME Runway 5R with the SMO transition. The FMS went into DR mode about half way from SMO to starting the turn to the northeast to intercept the localizer. The MAP still shows on the proper track; and there is little time to set up raw data to track the SMO 160 radial and set up the lead in radial. After a short time in DR the FMA shows heading HLD and the map shifts to show the aircraft right of course. An immediate left turn is required to not overshoot the localizer. This is especially dangerous due to the fact that an overshoot of the localizer put the aircraft heading directly towards very high terrain. Undetected this NAV failure and failure to intervene with heading select and rearming the ILS mode could lead to a serious GPWS/TERRAIN event. No prior DR mode annunciations were present during any of these flights until this point. The flights where this event occurred were (all different tail numbers) all in April.
Air Carrier Captain experiences loss of GPS signal on three separate occasions during approach to MMMX between SMO and the turn to intercept the Runway 5R localizer.