Southwest Airlines will keep Boeing 737 Max jets grounded until at least the end of May.
It has pulled the aircraft from flight schedules through May, extending its earlier timeline by more than one month, from April 20.
The extension will provide more certainty for customers.
"This will impact the lines in May, but, now that the decision has been made, we can construct our schedule without those flights well in advance in hopes to minimize the daily disruptions," the airline and its pilots union said in a joint release.
The 737 Max jetliner has been grounded worldwide after two deadly crashes within the space of five months.
Southwest is the hardest hit of any US airline with 34 new 737 Max jets in its fleet.
Although this is just a small percentage of its overall fleet of more than 700, it has still resulted in thousands of flight cancelations so far.
It has already scrapped nearly 3,000 flights in March due to the grounding.
In addition to this, a further 7,000 flights were canceled due to a combination of bad weather and a labor dispute with mechanics.
By extending the timeline the airline has reacted to a barrage of complaints on social media criticizing its policy of leaving it until the last minute before confirming cancelations.
"Independent of the timeline for a return of service of Max aircraft, the flight schedule revision is about returning to a normal operation and restoring a reliability that our customers our crews deserve and expect from Southwest,” the airline said.
American Airlines, which has 24 Boeing 737 Max jets, has pulled the aircraft from schedules until at least April 24.
