In April, Boeing provided a $425 million advance to support Spirit's liquidity. Spirit, Wichita's largest employer with around 12,800 full-time workers, previously disclosed it has spent all of that money, as well as the entirety of a $350 million bridge loan that was set up earlier this year.

"We would not be surprised to see another such arrangement be announced," a prominent Wall Street aerospace sector analyst said.

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.