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.

One week after Spirit AeroSystems announced it has "substantial doubt" about its ability to continue as a going concern, Boeing is offering help.

Shares of Boeing Co. ($BA) gained retail investor interest on Tuesday after the aerospace giant agreed to provide up to $350 million in advance payments to Spirit AeroSystems ($SPR) to stabilize its key supplier amid ongoing liquidity challenges.

Spirit AeroSystems signage near a Boeing 737 fuselage is seen here in January outside the Boeing manufacturing facility in Renton, Wash. Of late, both companies have seen their financial challenges enhanced by a Boeing machinists strike that lasted nearly two months.