American Airlines has confirmed it now expects the Boeing 737 Max to remain grounded until at least September 3rd.
The Fort Worth, Texas-based carrier had previously removed the aircraft type from its schedule until August 19th.
American originally planned to operate roughly 115 daily flights on the 737 Max.
However, there is no certainty the plane will return to schedules in September.
The FAA is currently working with manufacturer Boeing to certify software upgrades to the 737 Max following two fatal crashes in Indonesia and Ethiopia.
A combined 346 people were killed in the accidents five months apart.
Southwest Airlines, the biggest Max operator, has set August 5th for the plane to resume flights, while United plans for August 3rd.
In a statement American Airlines said it “remains confident” that the software updates, along with the new training elements Boeing is developing for pilots, will lead to recertification of the aircraft “soon”.
American added: “We have been in continuous contact with the Federal Aviation Administration, department of transportation, National Transportation Safety Board and other regulatory authorities, and we are pleased with the progress to date.”
Customers affected by the cancellations can be booked on other flights or can request a full refund, American Airlines added.