Widebody transport flight crew receives false egpws warning on low final approach.

Attributes
ACN	756235
Time
Date	200709
Place
Locale Reference	airport : vtbs.airport
State Reference	FO
Altitude	agl single value : 500
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tower : zzz.tower
Operator	common carrier : air carrier
Make Model Name	Widebody Low Wing 3 Turbojet Eng
Operating Under FAR Part	Part 121
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 150 flight time total : 9100 flight time type : 2255
ASRS Report	756235
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

We were established and stabilized on the ILS to runway 19R into bangkok; thailand. The WX conditions were clear with very good visibility. There were a few thunderstorms on the horizon. Approaching 400-500 ft above the ground; we received the egpws terrain warning 'terrain ahead pull up.' I was the PF and called for a go around. We executed the maneuver and advised ATC of the go around and why. After leveloff we discussed what happened and all 3 of us couldn't come up with a reason why the warning activated. We elected to try the approach again and discussed that if we received the warning again; and we were stabilized; and could guarantee safe terrain clearance that we continue to a landing. Once on the ILS to runway 19R we confirmed our path against the charts and ATC and again at 400-500 ft AGL the warning came on again. We were on the PAPI and GS and I could see that the terrain was not a factor; so I continued for the landing. We landed safely and upon block in we wrote the warning up in the logbook and found out from maintenance that there was a problem with the egpws computer.

Original NASA ASRS Text

Title: WDB FLT CREW RECEIVES FALSE EGPWS WARNING ON LOW FINAL APCH.

Narrative: WE WERE ESTABLISHED AND STABILIZED ON THE ILS TO RWY 19R INTO BANGKOK; THAILAND. THE WX CONDITIONS WERE CLR WITH VERY GOOD VISIBILITY. THERE WERE A FEW TSTMS ON THE HORIZON. APCHING 400-500 FT ABOVE THE GND; WE RECEIVED THE EGPWS TERRAIN WARNING 'TERRAIN AHEAD PULL UP.' I WAS THE PF AND CALLED FOR A GAR. WE EXECUTED THE MANEUVER AND ADVISED ATC OF THE GAR AND WHY. AFTER LEVELOFF WE DISCUSSED WHAT HAPPENED AND ALL 3 OF US COULDN'T COME UP WITH A REASON WHY THE WARNING ACTIVATED. WE ELECTED TO TRY THE APCH AGAIN AND DISCUSSED THAT IF WE RECEIVED THE WARNING AGAIN; AND WE WERE STABILIZED; AND COULD GUARANTEE SAFE TERRAIN CLRNC THAT WE CONTINUE TO A LNDG. ONCE ON THE ILS TO RWY 19R WE CONFIRMED OUR PATH AGAINST THE CHARTS AND ATC AND AGAIN AT 400-500 FT AGL THE WARNING CAME ON AGAIN. WE WERE ON THE PAPI AND GS AND I COULD SEE THAT THE TERRAIN WAS NOT A FACTOR; SO I CONTINUED FOR THE LNDG. WE LANDED SAFELY AND UPON BLOCK IN WE WROTE THE WARNING UP IN THE LOGBOOK AND FOUND OUT FROM MAINT THAT THERE WAS A PROB WITH THE EGPWS COMPUTER.

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.