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.