Narrative:

This flight into quito encountered multiple map shifts; a 'terrain' warning; and excessive tailwind on landing. Forecast: 150 degrees at 5 KTS 9999 scattered 040. 340 degrees at 10 KTS 9999 broken 036 broken 100. ATIS: 140 degrees at 8 KTS 10+ mi visibility 40 scattered 18/8 landing runway 35; takeoff runway 17. About 15 NM north of qit VOR at FL180 a map shift occurred. On the 'descent 3 VOR DME runway 35' passing 15000 ft on the qit 150 degree radial; another map shift was observed; approximately 1 mi. Raw data was closely monitored by the pilot monitoring throughout the approach and the aircraft remained within limits. On the inbound turn; the map shift appeared to increase as we rolled out on final in VMC with light winds at altitude. The position of the aircraft was significantly different versus the HSI display track. As normal in quito; the descent rate was higher than normal due to high altitude; high true airspeed and tailwind. On short final; inside of 2 mi; aligned with the runway (runway 35) and the VASI depicting '3 white and 1 red' (slightly high) a 'terrain' warning activated. I observed no terrain threat and the HSI erroneously displaying the runway versus the aircraft. I concluded the system inaccurately perceived the aircraft was not aligned to land on the runway and; therefore; the egpws activated. I disregarded the warning; disabled the system and continued the approach. Before and during the approach; quito approach and tower reported winds at or below 10 KTS. The aircraft touched down about 3000 ft due to some floating. However; at the ramp; we could clearly see and feel the winds were greater than 10 KTS. Station personnel commented that the winds were just 6 KTS when we landed (not sure how this was determined). However; I requested a call to the meteorological office for the latest observation: XA00Z; 150 degrees winds 13 KTS gusting to 23 KTS which seemed more accurate from our observations. Tower continued to report winds below 10 KTS. As usual; quito operations attempts to maximize payload given the runway in use and WX conditions. How can we accurately plan our maximum takeoff limit when the tower does not provide accurate WX information? I elected to use the 'improved climb takeoff performance APU to packs' data. Corrections were made for pressure altitude and only 5 KTS of headwind for a takeoff limit of 200000 pounds. Payload was reduced by 2000 pounds. At takeoff; tower reported winds of 150 degrees 8 KTS. Finally; the flight from sequ to ZZZZ is normally not dispatched with an alternate because the WX does not require it. However; I requested that an alternate be included on the flight release due to single runway in ZZZZ. No additional fuel was loaded in sequ to meet this request. It should be noted that in my opinion releasing this flight to an airport without sufficient fuel to divert in the event the runway closes in unwise. A runway closure can occur for many reasons and leaves the crew with few options. Recommendations: 1) identify the reason for map shifts in the vicinity of quito. 2) evaluate and determine the reasons for the discrepancies between approach/tower and the meteorological office WX reporting. 3) in the interim; stop using improved climb takeoff performance data. Stop using pressure altitude and headwind corrections to increase the maximum allowable takeoff weight until WX reporting accuracy can be assured. 4) dispatch all flts from sequ to ZZZZ with an alternate; regardless of WX. Please note; the following day on climb out from ZZZZ we got a map shift. The navaids tuned by the FMC was mnv and ilg. The navigation data for ilg showed 2 options: 110.3 S0210.2 W07953.5 or 110.3 S0209.1 W07952.8. It seems that the system has 2 locations for the same VOR causing map shifts. I am not sure if this was the same VOR that was tuned into quito causing the map shifts.

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Original NASA ASRS Text

Title: B757 FLT CREW DISCUSSES SEVERAL ISSUES CONCERNING SEQU; THE MOST SIGNIFICANT BEING FMC MAP SHIFTS CAUSING ERRONEOUS EGPWS WARNINGS DURING ARRIVALS AND DEPARTURES.

Narrative: THIS FLT INTO QUITO ENCOUNTERED MULTIPLE MAP SHIFTS; A 'TERRAIN' WARNING; AND EXCESSIVE TAILWIND ON LNDG. FORECAST: 150 DEGS AT 5 KTS 9999 SCATTERED 040. 340 DEGS AT 10 KTS 9999 BROKEN 036 BROKEN 100. ATIS: 140 DEGS AT 8 KTS 10+ MI VISIBILITY 40 SCATTERED 18/8 LNDG RWY 35; TKOF RWY 17. ABOUT 15 NM N OF QIT VOR AT FL180 A MAP SHIFT OCCURRED. ON THE 'DSCNT 3 VOR DME RWY 35' PASSING 15000 FT ON THE QIT 150 DEG RADIAL; ANOTHER MAP SHIFT WAS OBSERVED; APPROX 1 MI. RAW DATA WAS CLOSELY MONITORED BY THE PLT MONITORING THROUGHOUT THE APCH AND THE ACFT REMAINED WITHIN LIMITS. ON THE INBOUND TURN; THE MAP SHIFT APPEARED TO INCREASE AS WE ROLLED OUT ON FINAL IN VMC WITH LIGHT WINDS AT ALT. THE POS OF THE ACFT WAS SIGNIFICANTLY DIFFERENT VERSUS THE HSI DISPLAY TRACK. AS NORMAL IN QUITO; THE DSCNT RATE WAS HIGHER THAN NORMAL DUE TO HIGH ALT; HIGH TRUE AIRSPD AND TAILWIND. ON SHORT FINAL; INSIDE OF 2 MI; ALIGNED WITH THE RWY (RWY 35) AND THE VASI DEPICTING '3 WHITE AND 1 RED' (SLIGHTLY HIGH) A 'TERRAIN' WARNING ACTIVATED. I OBSERVED NO TERRAIN THREAT AND THE HSI ERRONEOUSLY DISPLAYING THE RWY VERSUS THE ACFT. I CONCLUDED THE SYS INACCURATELY PERCEIVED THE ACFT WAS NOT ALIGNED TO LAND ON THE RWY AND; THEREFORE; THE EGPWS ACTIVATED. I DISREGARDED THE WARNING; DISABLED THE SYS AND CONTINUED THE APCH. BEFORE AND DURING THE APCH; QUITO APCH AND TWR RPTED WINDS AT OR BELOW 10 KTS. THE ACFT TOUCHED DOWN ABOUT 3000 FT DUE TO SOME FLOATING. HOWEVER; AT THE RAMP; WE COULD CLRLY SEE AND FEEL THE WINDS WERE GREATER THAN 10 KTS. STATION PERSONNEL COMMENTED THAT THE WINDS WERE JUST 6 KTS WHEN WE LANDED (NOT SURE HOW THIS WAS DETERMINED). HOWEVER; I REQUESTED A CALL TO THE METEOROLOGICAL OFFICE FOR THE LATEST OBSERVATION: XA00Z; 150 DEGS WINDS 13 KTS GUSTING TO 23 KTS WHICH SEEMED MORE ACCURATE FROM OUR OBSERVATIONS. TWR CONTINUED TO RPT WINDS BELOW 10 KTS. AS USUAL; QUITO OPS ATTEMPTS TO MAXIMIZE PAYLOAD GIVEN THE RWY IN USE AND WX CONDITIONS. HOW CAN WE ACCURATELY PLAN OUR MAX TKOF LIMIT WHEN THE TWR DOES NOT PROVIDE ACCURATE WX INFO? I ELECTED TO USE THE 'IMPROVED CLB TKOF PERFORMANCE APU TO PACKS' DATA. CORRECTIONS WERE MADE FOR PRESSURE ALT AND ONLY 5 KTS OF HEADWIND FOR A TKOF LIMIT OF 200000 LBS. PAYLOAD WAS REDUCED BY 2000 LBS. AT TKOF; TWR RPTED WINDS OF 150 DEGS 8 KTS. FINALLY; THE FLT FROM SEQU TO ZZZZ IS NORMALLY NOT DISPATCHED WITH AN ALTERNATE BECAUSE THE WX DOES NOT REQUIRE IT. HOWEVER; I REQUESTED THAT AN ALTERNATE BE INCLUDED ON THE FLT RELEASE DUE TO SINGLE RWY IN ZZZZ. NO ADDITIONAL FUEL WAS LOADED IN SEQU TO MEET THIS REQUEST. IT SHOULD BE NOTED THAT IN MY OPINION RELEASING THIS FLT TO AN ARPT WITHOUT SUFFICIENT FUEL TO DIVERT IN THE EVENT THE RWY CLOSES IN UNWISE. A RWY CLOSURE CAN OCCUR FOR MANY REASONS AND LEAVES THE CREW WITH FEW OPTIONS. RECOMMENDATIONS: 1) IDENT THE REASON FOR MAP SHIFTS IN THE VICINITY OF QUITO. 2) EVALUATE AND DETERMINE THE REASONS FOR THE DISCREPANCIES BTWN APCH/TWR AND THE METEOROLOGICAL OFFICE WX RPTING. 3) IN THE INTERIM; STOP USING IMPROVED CLB TKOF PERFORMANCE DATA. STOP USING PRESSURE ALT AND HEADWIND CORRECTIONS TO INCREASE THE MAX ALLOWABLE TKOF WT UNTIL WX RPTING ACCURACY CAN BE ASSURED. 4) DISPATCH ALL FLTS FROM SEQU TO ZZZZ WITH AN ALTERNATE; REGARDLESS OF WX. PLEASE NOTE; THE FOLLOWING DAY ON CLBOUT FROM ZZZZ WE GOT A MAP SHIFT. THE NAVAIDS TUNED BY THE FMC WAS MNV AND ILG. THE NAV DATA FOR ILG SHOWED 2 OPTIONS: 110.3 S0210.2 W07953.5 OR 110.3 S0209.1 W07952.8. IT SEEMS THAT THE SYS HAS 2 LOCATIONS FOR THE SAME VOR CAUSING MAP SHIFTS. I AM NOT SURE IF THIS WAS THE SAME VOR THAT WAS TUNED INTO QUITO CAUSING THE MAP SHIFTS.

Data retrieved from NASA's ASRS site as of January 2009 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.