Fueled by an appetite for trans-Atlantic flights, Delta Air Lines (DAL) on Friday said air traffic in July rose 3% year-over-year, though load factor slumped slightly as demand struggled to keep pace with a ramp up in capacity.

Consolidated passenger unit revenue, known in the industry as Prasm, is a key growth metric for carriers. While revenue per mile increased 1.7%, the No. 2 U.S. carrier behind United Continental (UAL) boarded fewer passengers.

Atlanta-based Delta boarded 15.64 million, down 0.2% from 15.68 million a year ago.

The monthly results come a few weeks after Delta trumped Wall Street expectations for the second quarter as sales rebounded and the carrier streamlined operations to save costs.

Cargo demand fell 11% year-over-year during the quarter, partially offset by a 1% increase in quarterly passenger revenues.

Shares of the airline slumped about 1% in recent trade to $21.86.

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