Hordes of U.S. vacationers are back, crowding airports , filling up hotels and national parks. Airlines' second-quarter earnings should give some insight into what happens after the summer surge. Delta Air Lines kicks off second-quarter reporting before the market opens on Wednesday and will provide its outlook on travel for the late summer and fall. Its competitors report in the coming weeks. A surge in bookings this spring and summer, along with customers willing to pay higher air fares , provided welcome relief for U.S. airlines that together lost more than $35 billion last year. Airline executives have noted the recovery has been led largely by leisure customers traveling domestically, with that segment near 2019 levels. Nevertheless, analysts expect carriers to report losses again for the second quarter. Airline bosses' commentary are likely to drive the sector's next stock moves. U.S. airlines' share prices have struggled over the past month as jet fuel costs continued to climb and the fast-spreading delta variant of Covid-19 raised concerns about new cases. Delta and Southwest Airlines shares have each dropped by more than 9% over the past month. United Airlines shares lost more than 12% and American Airlines over 13%, while the S & P 500 added about 3% over the same period. But the sharp rebound in air travel demand isn't fully appreciated by the market, Deutsche Bank airline analyst Michael Linenberg said in a note this week. The U.S. airline industry is on track to return to profitability in the fourth quarter, and some airlines could get there earlier, he said. Here are four issues investors need to watch in airlines' second-quarter results. 1. Business, international travel Business travel is a key piece to restoring airlines to profitability, particularly after summer vacationers return home. Analysts don't expect the four largest U.S. airlines to post positive net income for the second quarter and while up sharply from last year, revenue continues to trail pre-pandemic levels. Corporate travelers are generally less price sensitive than leisure customers, snapping up last-minute tickets that fetch a premium. In unveiling its record 270-plane Boeing and Airbus order last month , United's chief commercial officer, Andrew Nocella, said that just 30% of United's revenue in 2019 came from its standard coach cabin. Business travel has been creeping back up, but it still remains far from pre-pandemic levels. United Airlines CEO Scott Kirby told CNBC last month that business travel is down 60% compared with before the pandemic, an improvement from March when that was off about 90%. He said he doesn't expect business travel to return to 100% of pre-pandemic levels until 2023. Long-haul international travel is still weak with U.S. travel restrictions still in place on many foreign visitors. Airlines have been strategically building up summer Europe schedules to countries like Greece, Spain and Italy, which have reopened their borders to U.S. and other international visitors . 2. Labor costs Airline executives will provide updates on their labor costs and hiring plans as demand recovers. Since last March, U.S. airlines have enjoyed a cushion of $54 billion in federal payroll aid in exchange for not involuntarily furloughing workers. Thousands of employees, at the companies' urging took buyouts or leaves of absence, leading to staffing shortfalls in some areas of the business, such as customer service lines as travel demand surged. Airlines, including American and Delta , are hiring workers back and seeking others. Meanwhile, airlines have already started hiring pilots again, or plan to this year, while flight attendants are also again in demand at some carriers, including Southwest . 3. Jet fuel prices Meanwhile, jet fuel prices are rising. U.S. Gulf Coast jet fuel was going for $1.9524 a gallon on July 2, the highest since Jan. 7, 2020, according to S & P Global Platts. "We expect 2Q21 fuel costs will outpace expectations and wouldn't be surprised if 3Q21 jet fuel guidance comes in ahead of where the sell-side is modeling," said Cowen airline analyst Helane Becker. Goldman Sachs said in a July 6 note that jet fuel would likely weigh on airlines' bottom lines this year, though it said it assumed "that a portion of the uptick in the fuel bill is passed on via revenue in the out years of our forecast when demand has recovered in more earnest." 4. Post-summer flying Airline executives will also provide updates on how much they plan to fly this fall. Revenue and yields will largely depend on how well they match flying to demand after the summer rush. Southwest last month said it expects its August capacity to be roughly in line with the same month of 2019, but carriers are expected to provide details about booking trends cropping up this fall, including holidays like Thanksgiving. -- CNBC's Nate Rattner contributed to this article.
Travelers arrive at main concourse of Denver International Airport in Denver, Colorado on Wednesday, July 7, 2021.
Hyoung Chang | Denver Post | Getty Images
Hordes of U.S. vacationers are back, crowding airports, filling up hotels and national parks. Airlines' second-quarter earnings should give some insight into what happens after the summer surge.