Argus downgraded shares of Delta Air Lines to hold from buy, citing weaker-than-expected quarterly earnings and a less-than-stellar outlook. Shares of the Atlanta-based carrier have shed nearly 24% year to date through Thursday's close. While Delta benefited from the rollback of Covid-19 travel restrictions and increased demand for international flights, it's also been hit by capacity reductions and staffing shortages, analyst John Staszak wrote in a Thursday note. That showed up in the airline's second-quarter earnings, released Wednesday, which revealed weaker-than-expected earnings per share. In addition, Delta projected only modest revenue growth in the third quarter. "We caution that airline stocks are volatile and suitable only for risk-tolerant investors," wrote Staszak. Going forward, Argus expects Delta and other airlines will grapple with pressure from rising expenses, including the cost of jet fuel. At the same time, ticket prices will likely level off as industry capacity expands. Argus reduced its 2022 earnings per share estimate for Delta to $3.00 from $4.25 and lowered its 2023 estimate to $6.10 from $6.50, driven by prospects for increases in unit costs. There is an upside chance that Delta could outperform, the firm said. "If unit costs are lower than we currently anticipate, we would consider returning the stock to our buy list," wrote Staszak. Other airlines are also being slashed by Wall Street. On Friday, Wolfe Research downgraded American Airlines to underperform from peer perform, given its high-end balance sheet leverage heading into an economic downturn.