Boeing Co. Chief Executive Dennis Muilenburg will acknowledge on Tuesday that the aircraft manufacturer made mistakes, as he appears at a congressional hearing on two 737 Max crashes that killed 346 people, according to written testimony made public on Monday.

"We have learned and are still learning from these accidents, Mr. Chairman. We know we made mistakes and got some things wrong," Muilenburg will tell the U.S. Senate Commerce Committee.

The testimony, which was first reported by Reuters and made public later on Monday, added that the company had made improvements to the now-grounded Max 737 airplane "that will ensure that accidents like these never happen again."