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 and up to $107 million from Airbus, giving the struggling supplier a lifeline as it burns cash after four consecutive years of losses.

Plans for a funding agreement with Boeing, first reported last week by Reuters, came days after Spirit issued a "going concern" warning - effectively putting investors on notice that it may be unable to pay its bills within the next 12 months.

A key supplier to both Boeing and Airbus, as well as smaller jetmakers like Bombardier, Spirit Aero has seen inventory pile up and deliveries slump in recent weeks following a recently settled strike at Boeing.

Airbus agreed to give Spirit up to $107 million in advanced payments in connection with deliveries of parts for the European planemaker.

Boeing, which plans to buy back its one-time subsidiary, needs Spirit Aero to remain on its feet as it seeks to revive jet production following the 53-day strike by most of its machinists, who are set to return to their jobs Tuesday.

Airbus also depends on Spirit Aero for important parts for its A350 and A220 jets and has warned that delays in receiving parts from Spirit could hurt A350 deliveries in 2025.

The supplier of fuselages for the Boeing 737 MAX and significant parts of the 787 and other models has said it expects to burn around $450 million to $500 million over the last three months of 2024 and first half of 2025.

"This agreement helps improve our liquidity. We continue to pursue a range of options to address our financial and spacing storage constraints and are working with our customers on these matters," Spirit spokesperson Joe Buccino said.

Boeing said it continued to work closely with Spirit to "stabilize our production system and help us deliver for our customers".

Spirit Aero's finances suffered when Boeing MAX production slumped after a Jan. 5 mid-air blowout on a new model.

A new process for vetting fuselages for flaws introduced in March further delayed Spirit's deliveries, leading to a pile-up of fuselages inside and outside the supplier's sprawling Kansas factory.

BOEING SHARES FALL

Spirit said the advances from Boeing would help it produce at rates required by the planemaker and tackle excess inventories and lower cash flows. It also cited "lingering effects brought on by the recent strike by Boeing employees".

It must technically repay the $350 million in 2026, though the takeover by former parent Boeing is tentatively expected to happen well before then, in mid-2025.