In this article DAL Follow your favorite stocks CREATE FREE ACCOUNT watch now VIDEO 4:35 04:35 Delta shares tumble after outlook falls short of estimates despite strong summer travel demand Squawk Box Delta Air Lines on Thursday forecast record revenue for the third quarter thanks to booming summer travel demand, but its forecast fell short of analysts' estimates as carriers discounted fares after expanding flights. In the current quarter, Delta expects sales to rise no more than 4%, lower than the 5.8% growth forecast by analysts polled by LSEG, and expects adjusted earnings per share of $1.

70 to $2 a share, short of the $2.05 a share analysts expected. Shares of Delta fell about 9% in premarket trading.

Other U.S. airlines were also trading lower.

The Atlanta-based carrier on Thursday kicked off an airline earnings season marked by packed planes but profits under pressure as costs rise and increased capacity weighs on fares. The Transportation Security Administration said it screened more than 3 million people for the first time on Sunday at U.S.

airports. Delta is a standout in the airline industry as the most profitable carrier, and Thursday's report is a sign that competitors, particularly those focused on the oversupplied U.S.

air travel market, could struggle this summer. Rival United Airlines , which reports results next Wednesday is trying to catch up to Delta's profitability, and both carriers have been racing to add more premium seats that fetch more revenue from c.