Dash 8-200
Flight Crew Air Transport Pilot (ATP)
Inflight Event / Encounter CFTT / CFIT
Flight Crew FLC complied w / Automation / Advisory
Environment - Non Weather Related; Aircraft
While on the LEGGO2 arrival at IAD; about 5 miles north of TICON Intersection at 4;000 MSL; we received a 'Terrain; Terrain Pull Up' warning. Due to the fact that we were night IMC and could not visually confirm terrain clearance; we called ATC while climbing to avoid any possible collision. After reaching 4;300 FT. MSL the warning and associated red light extinguished and we were able to return to our assigned altitude. We believed this to have been a false warning due to the fact that we were both on course and altitude for that particular section of the arrival. No further issues were encountered; and a normal landing was accomplished.Perhaps more frequent; or more thorough; inspections of our avionics/warning systems would possibly avoid this and other similar false indication situations. This should include exterior components and any associated seals. The rain may have played a large factor as water and electronics do not mix well.
A Dash 8 flight crew responded to an EGPWS terrain warning while level at 4;000 MSL; 5 NM north of TICON on the LEGGO RNAV STAR to IAD.