American's cancellations represent 1.5 per cent of its total flights each day of the summer.
The airline said it will bring the Max aircraft back on line as spares to supplement its operations once it is receritfied.
"But by extending our cancellations through the summer, we can. provide confidence to our customers and team members when it comes to their travel plans".
The tweet comes as the Chicago-based company has been under vast pressure after the crashes spurred an global grounding of the fleet and launched numerous federal investigations.
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To that, Boeing has responded with a video address by Muilenburg, who acknowledged investigators' findings that it faulty angle of attack sensor input activated Maneuvering Characteristics Augmentation System (MCAS), but retained that multiple reasons played a role in Flight 302 crash.
Federal regulators on Friday briefed pilots and US airlines on progress in restoring Boeing Co.'s grounded 737 Max to flight. USA safety regulators have to approve the fix and decide on new training for pilots.
The FAA initially said Boeing would complete the software fix "no later than April". The company had initially planned to submit its full package of software and training changes to the FAA for review by the first week of April, but the submission was delayed.
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.
"This has without a doubt damaged Boeing's reputation and we foresee a dent to the (Boeing) brand's value at over $12 billion", Chief Executive David Haigh said by email when asked about Trump's comments.