Bombardier celebrated the maiden flight of its largest commercial jet, the CSeries 300, on Friday amid lingering questions about the program’s long-term financial viability.

The successful flight at the company’s aerospace operation in Mirabel, outside Montreal, comes after multiple delays and C$2 billion ($1.6 billion) in cost overruns in its 11-year development, which has cost Bombardier about C$5.4 billion to date and depressed the company’s share price. The delays also contributed to the departure of Bombardier Chief Executive Officer Pierre Beaudoin on Feb. 12.
The jet can seat as many as 160 passengers and has garnered the bulk of the 243 firm orders Bombardier has collected for the plane and a smaller, 125-seat version, the CSeries 100. The smaller jet began flight tests in September 2013 and suffered an engine malfunction last spring during ground testing that forced some design changes. The CS100 is expected to enter commercial service later this year, followed by the CS300 in mid-2016.
Republic Airways Holdings, which operates regional flights for several major U.S. carriers, and leasing firm Macquarie AirFinance are the largest CSeries buyers. Both have ordered 40 of the planes, mainly the CS300.