By Brad Haynes

SAO PAULO, March 29 (Reuters) - Embraer's biggest passenger jet ever took to the skies more than three months ahead of schedule on Wednesday, giving the world's third-largest commercial planemaker more time to refine the aircraft before it enters service in early 2019.

John Slattery, head of commercial aviation for Embraer, said in an interview that the Brazilian company was maintaining its delivery timeline after a "very successful" first flight for the E195-E2, which was originally scheduled for the second half of this year.

"We do have a lot of buffer, clearly. And we are devoting that to maturing the aircraft before entry into service," Slattery said, adding that he expected the milestone to help sales campaigns for the 120- to 130-seat aircraft.

The new E195-E2 offers three more rows of seats and a more efficient engine than the current-generation E195, improving fuel burn by 24 percent per seat and directly challenging Bombardier Inc's new CS100.

Slattery said he saw healthy demand for the biggest member of the re-engined E-Jet family in Southeast Asia, Western Europe, North America and Latin America. He first hinted at the jet's early flight in a Reuters interview earlier this month.

The E195-E2 program remains on budget and in line with specifications, he added. Brazilian airline Azul Linhas Aereas Brasileiras SA, which has placed a firm order for 30 of the aircraft, will be the first operator of the new jet. (Reporting by Brad Haynes; Editing by Bill Rigby)