Southwest Airlines announced Tuesday that the Boeing 737 MAX will be removed from service until April -- a month later than originally planned.
The announcement comes the day after Boeing announced it will temporarily suspend production on the MAX in January while the fleet remains grounded because of safety concerns.
Southwest had 34 MAX planes when they were grounded in March. The carrier has continued to push back the return date for the planes.
Governments worldwide grounded the jets after two fatal crashes.
The first occurred in October 2018 when pilots of Lion Air Flight 610 lost control of the 737 MAX. The airliner crashed into the Java Sea 13 minutes after takeoff, killing all 189 people on board.
The second crash occurred in March. The 737 MAX operated by Ethiopian Airlines crashed six minutes after takeoff, killing 157 people.
Southwest Airlines announced Tuesday that it "continues to monitor information from Boeing and the Federal Aviation Administration on the impending 737 MAX software enhancements and training requirements."
The carrier said the enhancements "will support the safe operation of the MAX."
Southwest officials said pushing back the return for the MAX will reduce "last-minute flight cancellations and unexpected disruptions."
Customers will be notified if their planned flights will be affected, the company said.
Southwest estimates the additional delay of the 737 MAX return will remove 300 weekday flights.
Fort Worth-based American Airlines is also among the carriers to have its 737 MAX fleet grounded. In October, the airlines' flight attendants said they would not step foot on the planes.
The Associated Press and ABC News contributed to this report.