By David Shepardson, Allison Lampert and Tim Hepher (Reuters) -Spirit AeroSystems said on Tuesday it would receive up to $350 million in advance payments from its largest customer Boeing, giving the struggling supplier a lifeline as it burns cash after four consecutive years of losses.

Boeing has agreed to pay Spirit AeroSystems up to $350 million in advance to keep producing products for it as the fuselage supplier works through a liquidity crunch. The jet maker said Tuesday that the advance payments are intended to help Spirit address high levels of inventory and lower operational cash flows.

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

Boeing Co. will advance Spirit Aerosystems Holdings Inc. as much as $350 million as the planemaker gives its most important supplier a financial lifeline ahead of the planned purchase of the company.

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.