American Airlines (AAL) - Get Report has again extended the grounding of the Boeing (BA) - Get Report 737 MAX aircraft, leaving the controversial new jets locked up through Dec. 3.

The airline -- the world's largest by several measures -- had held off on resuming flights with the beleaguered high-tech jets several times earlier, last pinning the take off date for Nov. 2.  

With the Boeing aircraft tied up while safety checks, training and updates continue, American is canceling around 140 flights a day that would have been able to make use of its fleet of 24 of the 737 MAX planes. Some of the cancellations were flights scheduled on other aircraft whose routes were disrupted by the grounded jets. 

The airline's reservations and sales staff are working with customers whose flights are canceled or otherwise affected, said the airline.

"American Airlines remains confident that impending software updates to the Boeing 737 MAX, along with the new training elements Boeing is developing in coordination with our union partners, will lead to recertification of the aircraft this year," American Airlines said in a statement on Sunday.

The airline is working with the Federal Aviation Administration, Department of Transportation, National Transportation Safety Board and other regulatory authorities to prepare the jet for eventual takeoff. 

Airlines around the globe had begun holding off flights on Boeing 737 MAX jets after one had crashed in March in Ethiopia and another went down earlier over Indonesia last year in October. All passengers on the two crashes were killed.