US carriers American and Southwest Airlines have pushed back intended re-entry of service for the Boeing 737 MAX jets until March 2020.
American Airlines had previously said that it expected the aircraft to return to service in January, but its new guidance has said the grounding will continue until 4 March.
The airline anticipates cancelling "approximately 140 flights" per day.
In a statement, American said it "remains in continuous contact with the Federal Aviation Administration, Department of Transportation and Boeing. Based on the latest guidance, American anticipates that the resumption of scheduled commercial service on American's fleet of Boeing 737 MAX aircraft will occur March 5, 2020.
"Once the aircraft is certified, American expects to run exhibition flights, or flights for American team members and invited guests only, prior to March 5."
Meanwhile, Southwest, the Max’s biggest customer with 34 in addition to 41 that were expected to be delivered this year, is removing the planes from flight schedules from February 8 to March 6, 2020.
Southwest is cancelling about 175 daily flights during the period because of the aircraft’s grounding, the company said.
It's said that both airlines have accounted for nearly $1 billion in losses from the grounding of the airplanes.