NEW : Newark 's main airport will remain closed at least 8 a.m. . The passengers `` stayed calm '' during the emergency landing , the airline says . The plane was carrying 11 people from Warsaw to Warsaw . It landed on its belly after problems with its landing gear .
NEW : Warsaw 's main airport will remain closed overnight . The passengers `` stayed calm '' during the emergency landing , the airline says . The plane was carrying 231 people from Newark to Warsaw . It landed on its belly after problems with its landing gear .