Boeing's (BA) key supplier and acquisition target, has raised substantial doubt about its ability to continue as a going concern amid mounting losses, rapid cash burn and production challenges.  Its debt balance as of September 26 was $4.

Aircraft-parts supplier Spirit AeroSystems Holdings Inc. on Tuesday said that there was “substantial doubt” about its ability to keep running as a “going concern,” as losses, debt, and difficulties at jet maker Boeing Co.

In Q3, despite its quarterly revenues climbing slightly to $1.47 million from $1.43 million, Spirit AeroSystems’ costs ballooned to $1.7 billion, resulting in an operating and net loss of $350.1 million and $476.6 million, respectively.

Spirit AeroSystems, a key supplier to US planemaker Boeing, warned on Tuesday there was “substantial doubt” that the company would be able to continue as a going concern.

Wichita-based Spirit AeroSystems says it will soon end the furloughs of some of its employees and has no immediate plans to implement additional furloughs or layoffs after Boeing workers approved a contract offer on Monday.

"We retain a range of options and levers to address our financial and spacing constraints and are working with our customers on these matters," a Spirit spokesperson said.

U.S. supplier Spirit AeroSystems said on Tuesday in a quarterly filing that substantial doubt exists about the company's ability to continue as a going concern.