Boeing Co. failed to adequately consider how pilots respond to cockpit emergencies in its 737 Max safety assessment and may need to make changes to flight deck alerts, pilot procedures and training, the National Transportation Safety Board said.

The U.S. air accident investigator unveiled on Thursday several recommendations to the Federal Aviation Administration (FAA) following the fatal crashes of a Lion Air 737 Max in Indonesia and an Ethiopian Airlines 737 Max five months apart that killed a total of 346 people. The crashes led to the plane's grounding and raised questions about the FAA's certification of the new aircraft.

The crews in those crashes "did not react in the ways Boeing and the FAA assumed they would," said NTSB Chairman Robert Sumwalt.