Narrative:

On the river visual approach runway 18 at 4 DME and 1200 ft, we received a GPWS 'terrain, terrain, pull up' warning. We executed an immediate go around to the right (west) and climbed to 3000 ft as instructed by ATC. We checked system and altimeter settings, reloaded the approach and flew the exact same profile to a landing without incident. It was very dark with high scattered to broken clouds and good visibility (7-10 mi). Visually, we were clearly over the river and level above 1000 ft AGL. We had both vors set at dca 148 degree course for course guidance and DME. We had also loaded the 10 DME fix at 3000 ft and the 4 DME fix at 1200 ft on the mcdu for guidance. There was a slight tailwind on the approach, however, I arrived at 1200 ft a bit before 4 DME and was level at 1200 ft and configuring when I got the warning. We suspect possible momentary radar altimeter malfunction or a spurious input, but neither one of us noticed the radar altimeter indication at the time of go around. We have no evidence, but wonder if it is possible for some kind of interference such as cell phone or other transmission to have caused this anomaly.

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Original NASA ASRS Text

Title: A320 CREW HAD A GPWS TERRAIN WARNING AND EXECUTED A GAR AT DCA.

Narrative: ON THE RIVER VISUAL APCH RWY 18 AT 4 DME AND 1200 FT, WE RECEIVED A GPWS 'TERRAIN, TERRAIN, PULL UP' WARNING. WE EXECUTED AN IMMEDIATE GAR TO THE R (W) AND CLBED TO 3000 FT AS INSTRUCTED BY ATC. WE CHKED SYS AND ALTIMETER SETTINGS, RELOADED THE APCH AND FLEW THE EXACT SAME PROFILE TO A LNDG WITHOUT INCIDENT. IT WAS VERY DARK WITH HIGH SCATTERED TO BROKEN CLOUDS AND GOOD VISIBILITY (7-10 MI). VISUALLY, WE WERE CLRLY OVER THE RIVER AND LEVEL ABOVE 1000 FT AGL. WE HAD BOTH VORS SET AT DCA 148 DEG COURSE FOR COURSE GUIDANCE AND DME. WE HAD ALSO LOADED THE 10 DME FIX AT 3000 FT AND THE 4 DME FIX AT 1200 FT ON THE MCDU FOR GUIDANCE. THERE WAS A SLIGHT TAILWIND ON THE APCH, HOWEVER, I ARRIVED AT 1200 FT A BIT BEFORE 4 DME AND WAS LEVEL AT 1200 FT AND CONFIGURING WHEN I GOT THE WARNING. WE SUSPECT POSSIBLE MOMENTARY RADAR ALTIMETER MALFUNCTION OR A SPURIOUS INPUT, BUT NEITHER ONE OF US NOTICED THE RADAR ALTIMETER INDICATION AT THE TIME OF GAR. WE HAVE NO EVIDENCE, BUT WONDER IF IT IS POSSIBLE FOR SOME KIND OF INTERFERENCE SUCH AS CELL PHONE OR OTHER XMISSION TO HAVE CAUSED THIS ANOMALY.

Data retrieved from NASA's ASRS site as of July 2007 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.