The C919's maiden flight has been delayed at least twice since 2014 due to production issues.
China first gave the world a glimpse of the 158-seat plane in November 2015 at a roll-out ceremony in Shanghai.
The aircraft is a symbol of China's ambitions to break into a duopoly enjoyed by Western giants Airbus and Boeing Russia is developing a similar jet.
China Eastern Airlines is the launch customer for the plane, which is powered by engines from French-U.S. supplier CFM International, jointly owned by General Electric and Safran.
A third source said that COMAC had initially aimed to fly the C919 to coincide with the first such Chinese-European safety event but that the date had slipped into the first week of May.
(Reporting by Tim Hepher and Brenda Goh; Editing by David Clarke and Hugh Lawson)
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)