Southwest Airlines Co, the world's largest MAX operator, and American Airlines Group Inc with 34 and 24 MAX jetliners respectively, have removed the aircraft from their flying schedules into August. In early April, the company took the extraordinary step of cutting its 737 Max production rate from 52 per month to 42.
The model has suffered two deadly crashes in a matter of months, the first last October in Indonesia with the death of all 189 people on board and then in Ethiopia on March 10, killing all 157 aboard.
In a letter to pilots and employees, American Airlines President Robert Isom and CEO Doug Parker said the airline is confident that Boeing and the FAA will recertify the Max jet before mid-August, at which time the airline would bring the planes back into service as spares to supplement its operations throughout the summer.
United Airlines, with 14 MAX jets, has largely avoided cancellations by servicing MAX routes with larger 777 or 787 aircraft, but the airline president, Scott Kirby, warned last week that the strategy was costing it money and could not go on forever.
The airline's CEO Doug Parker and President Robert Isom issued a statement saying it would cancel 115 flights daily through August 19, representing approximately 1.5 of the airlines' flying each day during the summer.
They added that the airline has been in close contact with the FAA, the Department of Transportation, the National Transportation Safety Board and global regulators and are "pleased with the progress so far".
The FAA initially said Boeing would complete the software fix "no later than April". Preliminary investigations have pointed to problems with an anti-stall feature.
Park said canceling the flights now will help the airline plan for its busiest travel season of the year, CNBC reported.
Boeing is working on proposed software updates that would prevent the repeated triggering of a system that can drive the plane's nose down. In the previous weeks, Boeing pilots have flown 96 test flights, totalling 160 hours with the new software and will operate more flights in the coming weeks to prove that the software fix works.
American explained on its website that not all flights previously scheduled on a MAX would be cancelled, because the airline planned to use other aircraft for some flights.