Boeing's acquisition of Spirit AeroSystems, a deal valued at $8.4 billion, is proving more costly than initially anticipated, with the jet maker identifying substantial undisclosed liabilities since the December closing.

The financial strain emerged after Boeing took ownership, revealing financial obligations that were not apparent during the initial assessment of the deal. This situation has led to the acquisition bleeding red ink, indicating a negative financial return for Boeing.

The acquisition was aimed at integrating Spirit AeroSystems more closely into Boeing's manufacturing operations, potentially streamlining production and improving quality control for key aircraft components. However, the unexpected liabilities have introduced significant financial challenges, complicating Boeing's efforts to manage its costs and production timelines.