WASHINGTON (NEXSTAR) — Boeing’s CEO faced investors and reporters after more safety concerns were revealed over the weekend – indicating Boeing wasn’t transparent with airlines about safety features on the jets that were involved in two deadly crashes.

“All of us at Boeing are deeply sorry for the loss of life,” said Boeing CEO Dennis Muilenburg. He said the company will make changes to its 737 Max 8 jets.

Investors and reporters grilled him about the failure to identify a safety issue and warn its airline customers until after the disasters.

“You don’t have to have 300 plus people die every time to find out that something is unreliable,” an investor said.

The company said it will rework anti-stall software, which appears to have played a part in both deadly crashes.

“The U.S. government under the FAA’s leadership is also doing an independent review of certification processes,” Muilenburg said.

But he would not admit that Boeing made mistakes in design or safety certification of the planes and seemed to cast blame on the cockpit crews.

“When we design a system, understand that those systems are flown in the hands of pilots.”

Several pilot associations say they want pilots to have full simulator training on the Max 8 jets before they fly with passengers. But Boeing says that’s not what they’re doing.

“We believe that the right answer right now is computer based training. And then as part of the recurring training that pilots might do downstream, give them options for simulator training,” Muilenburg said.

He did not give a timeline for getting the planes back in the air.