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.

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.

The airframe manufacturer will get a new cash infusion from its major customer to ensure it can remain financially stable and maintain inventory, reduce operating expenses,