The airline said https://www.sec.gov/Archives/edgar/data/92380/000009238019000073/coverpage06-19x19.htm in a regulatory filing it now expects second quarter fuel efficiency to decrease in the 1% to 2% range, compared with its previous forecast of flat to down 1%, reflecting the impact of the grounding of its Boeing 737 MAX 8 aircraft through Aug. 5.

Southwest last week joined larger rival American Airlines in extending its removal of Boeing's currently grounded MAX planes from its schedules until the start of September.

(Reporting by Sanjana Shivdas in Bengaluru; editing by Patrick Graham)