The grounding of the Max 9 fleet and supply chain issues are significant operational challenges for United Airlines. These factors can lead to increased costs, delays, and reduced capacity, which in turn may negatively impact the company's financial outlook and investor sentiment in the short term. The direct mention of a 'downward bias to our 2024 spend' suggests a cautious approach to capital expenditure, which could be interpreted by the market as a sign of potential financial strain or a conservative financial strategy.