American Airlines has pushed back the date on which it expects to resume Boeing 737 Max flights to 16 January, six weeks later than it previously anticipated.
Despite the delay, however, American is expressing optimism in the likelihood that the Federal Aviation Administration will clear the aircraft to fly before year-end.
American had previously anticipated resuming some 737 Max operations on 4 December.
"American Airlines anticipates that the impending software updates to the Boeing 737 Max will lead to re-certification of the aircraft later this year and resumption of commercial service in January 2020," the airline says.
The airline and others have repeatedly pushed back the date on which they expect the Max will return, each time cancelling more flights in the process.
American says that on 16 January it "expects to slowly phase in the Max for commercial service and will increase flying on the aircraft throughout the month and into February".
The move comes amid continued uncertainty about how and when the 737 Max will return to the skies.
Signals have suggested the FAA may indeed clear the aircraft this year, as Boeing has repeatedly insisted.
But other regions' regulators, especially those in Europe, have expressed hesitation to rubber-stamp the FAA's approval, suggested various agencies may clear the aircraft on different timetables.