Senate panel grills Boeing CEO over flaws in MAX jet

The updated MCAS software will compare information from both "angle of attack" sensors before activating and will respond only if data from both sensors agree. In addition, MCAS will activate only once, and the pilot can counteract the anti-stall device by using the plane's control column alone, the CEO said.

The flight recorder, or "black box" recovered from both planes after the crashes showed that multiple alarms were activated prior to the accidents, and the automated anti-stall device sent the planes on a roller-coaster ride of steep climbs and sharp drops as the flight crews struggled to regain control.

Boeing's CEO said the company has devoted more than 100,000 hours to re-engineering and testing the anti-stall system and has made more than 814 test flights plus numerous flight simulator sessions with 545 participants from 99 customers and 41 global regulators.

"We have been challenged and changed by these accidents, and we are improving as a company because of them," Muilenburg said. "We have established a permanent aerospace safety committee of our board of directors."

Reuters contributed to this story.