An American Airlines Boeing 737 MAX 8 flight from Los Angeles lands at Reagan National Airport. Photo for illustrative purposes Image Credit: Reuters

American Airlines said Sunday it will extend flight cancellation through April 24 because of the grounding of the Boeing 737 Max after two fatal crashes since October and cut some additional flights.

American, the largest US carrier, said it is cancelling about 90 flights a day. American is the second-largest US operator of the Max in the United States with 24 jets, behind Southwest Airlines with 34.

American said earlier this month it was flying about 85 flights a day out of its 6,700 daily departures on 737 Max planes when the grounded was announced.

The airline said it was making the announcement "to provide more certainty to our customers and team members and better protect our customers on other flights to their final destination." Boeing Co is expected as early as Monday to formally disclose a planned upgrade to its anti-stall system to the Federal Aviation Administration (FAA) that has been in the works since October's Lion Air crash but still needs approval from US regulators.

The FAA has said it plans to mandate the upgrade by April, but it is still not clear if the upgrade will address any issues after the March 10 Ethiopian Airlines crash.

American, Southwest and United Airlines were all meeting with Boeing this weekend to review the software upgrade, Reuters reported Saturday.

The FAA said earlier the "design changes" would result in flight control system enhancements that will provide "reduced reliance on procedures associated with required pilot memory items." Reuters reported Thursday the upgrade will include a previously optional warning light. Many airlines, including American, already had the optional light.