The significant investments made by Spirit AeroSystems to stabilize 737 production in Q4, as mentioned by the CFO, resulted in unfavorable cumulative catch-up costs. This financial strain could potentially lead to a negative short-term impact on the company's stock price, as investors may react to the increased costs and the implications for future profitability.

While the article directly mentions Spirit AeroSystems' investments to stabilize 737 production, Boeing (BA) may experience indirect effects due to its close relationship with SPR as the manufacturer of the 737. The impact on Boeing's stock is less direct and may depend on broader market perceptions of the 737's stability and future production efficiency.