American Airlines Group Inc said on Friday it is extending cancellations of Boeing Co 737 MAX flights through March 4, 2020, mirroring an earlier announcement by Southwest Airlines.

American had previously canceled about 140 flights a day through January 15 and now expects a return to service on March 5.

Southwest said on Friday it would remove Boeing 737 MAX jets from its schedule until March 6, 2020, just shy of the one-year anniversary of an Ethiopian Airlines crash of the jet that led to a worldwide grounding.

Boeing Co is facing increasing hurdles in obtaining approval to return the plane to service before the end of this year as it has targeted.

It's reported that this week U.S. and European regulators will need to return to a Rockwell Collins facility in Iowa to complete an audit of Boeing's software documentation after regulators found gaps and substandard documents. Boeing has confirmed it must submit revised documentation.

That has thrown into question when Boeing would be able to complete a certification test flight. The Federal Aviation Administration has said it would not unground the planes until 30 days after that flight occurs.

(With input from Reuters)