The airlines are preparing for a lot of customers, but there are limits to how much they can improve their service. As air travel begins to pick back up, airlines are confident in their financial future. However, staffing shortages threaten to put a damper on things. This is especially true for smaller carriers and vendors. United Airlines’ CEO Scott Kirby stated that beyond the airlines’ own workforce, they require sufficient numbers of air traffic controllers, security agents, and fuel vendors. All of these constraints make it difficult to have a reliable schedule.

The airline executives say that they are seeing a lot of demand for travel in the spring and summer, but they are being cautious about how many flights they schedule so that they don’t end up overbooked like they have in the past. The airlines are doing well financially, with all of them making profits or projecting that they will in the near future. However, they are struggling to find enough workers to keep up with the demand.

Alaska Airlines is reducing the number of flights it operates this month by 2 percent due to a shortage of trained pilots, which has resulted in a number of last-minute cancellations. This is similar to what other airlines have done after a difficult start to the year. Smaller airlines that provide regional flights for the major airlines are having difficulty finding enough pilots to replace those who have been hired away by the larger carriers.Mr. Isom said that there are some industry-specific constraints on growth in the near term, notably related to pilot and aircraft supply. He said that American had hired 600 of the 2,000 pilots it hopes to bring on board this year, and that the airline is rapidly training them with the hope of having all of its planes back in use by the end of the year. In all, American has expanded its work force by 12,000 employees, or 10 percent, since last summer. Delta said last week that it had added about 15,000 workers since the start of last year. United has hired 6,000 this year. But as of February, none of the major carriers had returned to prepandemic employment levels, according to federal data. Industrywide, airlines employed more than 739,000 part-time or full-time workers in February, down about 2 percent from the same month in 2020. And airlines may struggle to staff up further. Mr. McNally said that it’s a competitive market out there, and that the airlines are forced to compete in a broader economy. He said that airlines face other challenges, too, including rising fuel prices.

American expects fuel prices in the second quarter to be about 30 percent higher than in the first, while United and Delta have said prices could rise as much as 20 percent. Last week, the price of jet fuel in North America was 20 percent higher than it was a month earlier and up 141 percent from a year ago, according to the Platts Jet Fuel Price Index. Despite the challenges, the industry remains broadly optimistic, largely because skyrocketing fares do not seem to have curbed the appetite for travel. For the second quarter of this year, American expects revenue to be about 6 to 8 percent higher than in the same quarter of 2019 — even though it expects capacity to be down 6 to 8 percent from the 2019 quarter. Airlines say customers aren’t just willing to pay higher fares — many are also shelling out even more money for premium upgrades like seats with more legroom. Airlines are particularly optimistic about recent improvements in corporate travel, a lucrative part of the business. Companies had been slow to send employees on work trips throughout the pandemic, but that appears to be changing quickly as offices reopen and companies lift such restrictions. The carriers said corporate travel had reached 70 to 80 percent of its 2019 level.

The Global Business Travel Association conducted a poll this month that showed that 86% of companies now allow employees to travel domestically for nonessential business, a 13% increase from February. The number of businesses that allow nonessential international travel has also increased, to 74%. This is a 26-point jump from February. Suzanne Neufang, the association’s chief executive, said in a statement that there is high levels of optimism and employee willingness to travel for business. American Airlines said that the way people travel has changed, too, perhaps for good. In the past, about 20-25% of the airline’s trips were for travel that combined business and pleasure. That share has increased over the past six months, to 50-55%. Vasu Raja, American’s chief commercial officer, said that “the nature of what we call leisure demand and business demand is changing.”

The airline industry hit another milestone this week when the federal mask requirement ended on public transportation. Both American and United said that they haven’t seen any significant change in bookings after dropping the mandate on Monday, although several surveys have suggested that passengers generally support the requirements. According to a poll by The Associated Press-NORC Center for Public Affairs Research, 56 percent of adults surveyed over the weekend said they support requiring masks on public transportation, with 24 percent opposed. International travel, which is another profit driver for airlines, is also showing signs of recovery. Consumers are traveling abroad in greater numbers, particularly between Europe and the United States, as travel restrictions are lifted and virus infection rates remain low, airlines said.

American Airlines said on Thursday that revenue from international travel had reached about 60 percent of prepandemic levels in March. The airline said it was seeing customers book more travel to South America and across the Atlantic, with many willing to buy premium seats, making up somewhat for a lack of international corporate travel. Travel to Asia continues to lag, though, because of health restrictions. United and Delta reported similar trends. But there is hope that the international rebound will be swift as countries open back up. Delta’s president, Glen Hauenstein, said last week that the airline expected flights to South Korea to grow to more than 90 percent full by June, up from about 50 percent full in March, after the country loosened travel restrictions this month. “When countries reopen, we see a rapid restoration of demand,” he said.