The Federal Aviation Administration is reviewing changes Boeing made to the planes but has not yet approved them to reenter commercial service. Regulators around the world ordered airlines to stop flying the planes last March after two fatal crashes — in Indonesia in October 2018 and in Ethiopia less than five months later — killed all 346 people on the two flights.
After months of overly optimistic forecasts from Boeing, the company ousted Dennis Muilenburg as CEO in December. A month later, it estimated the planes would be cleared to fly in mid-2020.
Because airlines need at least a month to train pilots — for which Boeing now recommends simulator training — and perform other tasks to get the planes ready to fly commercially, it could take weeks after federal approvals to return the jets to schedules.
Southwest, which operates an all-Boeing 737 fleet, pulled the planes from its schedules through Aug. 10, from a June 6 target previously.
"We remain confident that, once certified by the FAA, the enhancements will support the safe operation of the Max," the airline said.
That means the cancellation of about 371 weekday flights from peak schedules of 4,000 flights a day, the airline said.
Southwest said the Max grounding cost it $828 million in operating income last year. The company reached a compensation agreement with Boeing last year, but the cost could continue to climb as the grounding wears on.
Southwest had 34 Max planes in its fleet at the time of the grounding and expected to have 75 by the end of last year and 38 delivered this year. Boeing has halted deliveries and production of the planes because of the grounding.