Boeing Co may carry out a certification test flight of its grounded 787 Dreamliner with a revamped battery system on Friday, a key step toward returning the state-of-the-art aircraft to flight, a U.S. government official said on Thursday.

The official, who was not authorized to speak on the record, said the certification test could be carried out on Friday if all remaining ground-based tests were completed on Thursday.

All 50 787s in service worldwide were grounded in January after problems with the airplane's lithium-ion batteries on two separate aircraft.

(Reporting By Andrea Shalal-Esa; Editing by Gary Hill)