American Airlines is extending flight cancellations into mid-August because of the Boeing 737 Max grounding.
American, the world's largest airline, decided to extend cancellations from early June through to August 19, to help plan ahead for the busy summer travel season.
Southwest Airlines last week also extended flight cancellations for 737 Max planes from June until August.
'Based upon our ongoing work with the Federal Aviation Administration (FAA) and Boeing, we are highly confident that the MAX will be recertified prior to this time,' American Chairman and CEO Doug Parker and President Robert Isom said on Sunday in a message to airline staff.
'But by extending our cancellations through the summer, we can plan more reliably for the peak travel season.'
Approximately 115 flights a day will be cancelled through to August 19, representing about 1.5% of the airline's total daily flights, they said.
The airline has 24 737 Max jets in its fleet. American has previously said that all flights that were originally scheduled on a MAX plane will not be cancelled, with some being substituted with other aircraft.
The 737 Max was grounded in March after one of the planes flown by Ethiopian Airlines crashed, killing everyone on board. It was the second accident involving the jet model in less than six months, after another flown by Indonesia's Lion Air crashed last October. The crashes killed 346 people in total.
The causes of the crashes are still being investigated, but the focus has been on an automatic safety feature that may have forced the nose of each plane lower when it incorrectly sensed the plane was in danger of going into a stall.
Boeing and the FAA said they are working on an upgrade of the 737 Max software to deal with that safety feature.
Boeing CEO Dennis Muilenburg said on Thursday the planemaker is closing in on a fix for the software, and a majority of the 50 customers that have ordered 737 Max planes have had a chance to test it using a flight simulator.
He added that the update will make the plane 'even safer' because it will prevent 'erroneous' sensor readings.
'It's our responsibility to eliminate this risk,' Muilenburg said.
Muilenburg did not say when 737 Max planes may begin flying again.
Boeing announced earlier this month it was cutting the production rate for all of its 737 planes from 52 a month to 42 amid the worldwide grounding.