It’s been a year since a Lion Air Boeing 737 MAX crashed, the first of two accidents that killed 346 people. On Tuesday, Boeing CEO Dennis Muilenburg appeared on Capitol Hill, admitting the company made some mistakes and pilots need more information about the plane.

“These two accidents occurred on my watch and I have a keen sense of responsibility,” Muilenburg, who was stripped of his title as Boeing chairman, told reporters.

"In the months since the accidents, there has been much criticism of Boeing and its culture. We understand and deserve this scrutiny," he told the Senate Commerce Committee.

The plane has been grounded since the second crash, that of an Ethiopian Airlines flight in March that killed 157 people. The Lion Air flight went down in the Java Sea in Indonesia, killing the 189 passengers and crew aboard. The crashes were linked to a stabilization system that malfunctioned and kept pointing the planes’ noses down.

Lawmakers are weighing changes in aviation laws, especially related to how planes are certified as a result of the crashes. There have been allegations the Federal Aviation Administration and plane manufacturers have too cozy a relationship.

Indonesian investigators said last week Boeing didn’t understand the risks their 737 MAX software posed.

As Muilenburg testified for two hours about the company’s effort to fix the software and other factors that led to the fatal crashes, family members holding pictures of the victims sat just three rows behind him. Sen. Richard Blumenthal, D-Conn., described the 737 MAX as a “flying coffin” and accused Boeing executives of trying to shift blame to the pilots.

Muilenberg said he was unaware of emails between a former Boeing pilot and the Federal Aviation Administration indicating he had convinced regulators to delete information about the flight-control system implicated in the crashes.

Blumenthal said the crashes were “the result of a pattern of deliberate concealment.”

“Those pilots never had a chance. These loved ones never had a chance,” he said. “They were in flying coffins as a result of Boeing deciding it was going to conceal MCAS [maneuvering characteristics augmentation system] from the pilots.”

The MCAS malfunctioned on both planes because of faulty data from a sensor, which measured the angle of attack. Many pilots complained after the crashes they weren’t even aware of the system.

Muilenberg is to appear before the House Transportation and Infrastructure Committee Wednesday. It was unclear when the 737 MAX would be allowed to return to service.