Two officials of Riggs Bank were believed to have been  on a plane carrying Commerce Secretary Ronald Brown and nine other business   executives when it crashed Wednesday near Dubrovnik, Croatia.   
Paul Cushman 3d, chairman and chief executive of Riggs International  Banking Corp., a unit of the Washington bank, and Nancy Tuomey, vice   president of a Miami-based Riggs subsidiary, were part of the delegation   traveling with Mr. Brown to explore business possibilities in the war-torn   Balkans.       
  
An official at Riggs International confirmed that Mr. Cushman and Ms.  Tuomey were supposed to be on the plane. But government and bank officials   could not confirm whether the two actually boarded the flight. "We don't   know their whereabouts right now," the bank official said.     
A Defense Department official said the chances anyone survived the  accident are "slim to none." Rough weather was believed to have caused the   crash.