Teams from the three US airlines that own 737 MAX jets were heading to Boeing’s factory in Renton, Washington, to review a software upgrade.
The factory visits indicate Boeing may be nearing completion of a planned software patch for its newest 737.
Boeing and the Federal Aviation Administration, which must approve the software fix and new training, are under U.S. and global scrutiny.
The Allied Pilots Association (APA), which represents American Airlines pilots, said it has been in talks with Boeing, the FAA and airlines to get the airplanes flying again as soon as possible, albeit with an acceptable level of safety.