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.

Spirit AeroSystems said on Tuesday it would receive up to $350 million in advance payments from its largest customer Boeing and up to $107 million from Airbus , giving the struggling supplier a lifeline as it burns cash after four consecutive years of losses.