Shares in United Airlines (UAL -11.54%) were down as much as 11.4% today due to market volatility and investors digesting Delta Air Lines' (DAL -11.14%) earnings report and commentary the day before. A challenging environment United Airlines will report its first-quarter 2025 earnings on April 16, and if Delta's earnings are any indication, United's management is highly likely to report deteriorating conditions. Both airlines had already alerted the market to the uncertainty created by tariffs negatively impacting bookings. For example, in early March, Delta Air Lines management told investors that its first-quarter revenue growth would come in closer to 4% compared to previous guidance for growth of 7% to 9%. Ultimately, Delta's revenue growth came in at 3.3%. Delta's CEO Ed Bastian said "uncertainty around global trade" meant that growth had "stalled" with consumers and corporate travel negatively impacted. On a brighter note, he claimed that its international, premium, and loyalty-based revenue displayed "greater resilience." Delta declined to update its full-year guidance due to the uncertain market conditions. What it means for United Airlines investors Delta's commentary on international and premium travel holding up provides some comfort, but the weakness in Delta's main cabin revenue is highly likely also reflected in United's outlook. However, long-term investors were given more comfort as Delta's management said it would reduce capacity growth in the second half of the year in response to market conditions. That's a positive sign as it indicates an industry acting in a disciplined manner when a slowdown occurs. Investors' primary near-term concern is stabilizing the trade conflict so the air travel industry can continue recovering from the lockdown periods.