Ahead of the peak summer travel season, the airlines face the likelihood that pilots will have to be trained on simulators before the jets return.
The problem has worsened for carriers because they had expected Boeing to deliver more jets at the time of the grounding last March, after the second of two fatal crashes that killed 346 people within five months. Regulators, who ordered airlines to stop flying, have repeatedly said they have no firm timeline to approve the planes again for commercial flights.
Boeing earlier this month said it would recommend pilots undergo simulator training before airlines start flying the planes again, a process that could further delay the Max's return to service and one that promises to add to Boeing's costs.
Southwest, which operates an all-Boeing 737 fleet — mostly older models — reached a compensation agreement last month with Boeing over the grounding, but it could receive more as the flight ban wears on.
Southwest is pulling the planes through June 6, an effort to "reduce last-minute flight cancellations and unexpected disruptions." The Dallas-based carrier plans to remove 330 weekday flights from its peak-day schedules of more than 4,000 flights, 50 more flights than when it expected to have the planes back in service by early April.