MD-82
Flight Crew Air Transport Pilot (ATP)
Human-Machine Interface; Troubleshooting; Workload; Confusion
Aircraft Equipment Problem Critical
Flight Crew Overcame Equipment Problem; Flight Crew FLC Overrode Automation
Environment - Non Weather Related; Airport; Aircraft
During the approach [in mountainous terrain] we experienced a dead reckoning warning on the GFMS and a map shift. The Captain briefed me that he would fly in raw data. After passing the VOR we tracked outbound on the 168 degree radial [as charted]. I advised the Captain that the GFMS says the course is to the right but raw data had us on course. The weather was clear with a full moon as we joined the ILS and had the runway in sight we were on the glideslope and VASI. We were cleared to land and about half way down the ILS when the EGPWS started warning 'Terrain; Terrain pull up' and the NAV display showed red but it was a false warning.We confirmed our position and landed. I later told the Captain the NAV display showed the runway far to the left even though we were on the ILS perfectly lined up. Due to the map shift the GFMS and the EGPWS gave us false information.
Approaching [the IF VOR] the PFD displayed DR and the GFMS displayed DEAD RECKONING and the subsequent message RAIM LIMIT EXCEEDS 1.0. Since I previously have encountered intermittent DR messages in the past on this particular approach; that have quickly cleared themselves; I had pre-briefed the First Officer that I would have the VOR and the 168 degree course pre-loaded as a raw data backup. I switched to VOR and advised the First Officer that I was now using raw data.We were slowing; descending and configuring during this entire time. Approaching the turn point for the lead radial; I advised the First Officer that I was switching to the ILS frequency and course and that I had visually acquired the airport and runways. I started my turn inbound to the ILS; started our descent to 8;800 feet; and armed the ILS on the DFGS.I reached down and switched the EGPWS to OVERRIDE and continued visually. The remainder of the approach was normal and uneventful. At no time did the controllers say anything out of the ordinary.
As they began their approach the MD-82 flight crew received a DR (dead reckoning) warning they switched from GFMS guidance to raw data. After established inbound with the ILS and VASI centered and the runway in sight they received an EGPWS TERRAIN warning which they silenced and proceeded to a safe landing. At the time of the warning the NAV display showed them well to the right of the runway.