Delta leads the airline sector lower after warning of lower fare discounting

Delta Air Lines Airbus A330-300 airplane

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Delta Air Lines (NYSE:DAL) slid on Thursday after rattling investors with cautious guidance.

Revenue was up 7.2% year-over-year to a record tally for the quarter of $16.7 billion. Premium revenue increased 10%, with premium unit revenues positive year-over-year. Loyalty revenue was up 8%, driven by co-brand