Boeing and the aerospace supply chain have navigated a costly labor strike with surprising ease. One of Boeing’s key suppliers, however, has run into significant trouble. Tuesday, fuselage supplier Spirit AeroSystems filed its quarterly report with the Securities and Exchange Commission.

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.

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.

Spirit AeroSystems is warning that its business viability remains in doubt, saying its cash reserves are drying up due to Boeing's sharply reduced production rates and to other factors driving steep losses on its Airbus and Boeing programme work.

"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.

The designer and manufacturer for commercial and defense aircraft said its liquidity has been affected in part by the strike at Boeing and limitations on that company’s ability to increase production.

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.

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.

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.