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 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.