American Airlines said on Wednesday it was "unaware" of some functions of an anti-stall system on Boeing's 737 MAX until last week.
Boeing and the U.S. Federal Aviation Administration (FAA) issued guidance on the system last week after a Lion Air jet crashed in Indonesia on Oct. 29, killing all 189 people on board.
"We value our partnership with Boeing, but were unaware of some of the functionality of the Maneuvering Characteristics Augmentation System installed on the MAX 8," an American Airlines spokesman said.
He said American Airlines must ensure its pilots are fully trained on procedures and understand key systems on the jets they fly.
"The work with the FAA and Boeing is on-going, and we will continue to keep pilots informed of any updates," the spokesman said.
