A Boeing engineer was concerned that the troubled 737 Max, years before it came to market, had a flight-control system that lacked sufficient safeguards, according to a document released Wednesday during a tense hearing in the House where lawmakers hammered the manufacturer's CEO over two fatal crashes of the jetliners, and repeatedly asked why he hasn't resigned or given up his pay.

Other documents released during the hearing included a Boeing manager's concerns about the high pace of production at a Boeing 737 production facility months before the crashes, while another document highlighted assumptions about how quickly pilots could respond to a malfunction on board.

The more than five-hour hearing Wednesday capped two days of sharp questioning by lawmakers of beleaguered CEO Dennis Muilenburg on Capitol Hill this week. Those included calls that he forgo his salary this year and questions over why he hasn't resigned in the wake of the crashes that killed 346 people.

Muilenburg earned total compensation of just under $23.4 million for 2018, according to a Securities and Exchange Commission filing.

Boeing isn't handing out executive bonuses this year, a spokesman told CNBC.

The hearings underscored concerns that federal regulators didn't do enough to police the plane's design before they certified it as safe for passengers in 2017. They appearances also put Boeing's CEO on the defensive about flight safety assumptions and raised questions that the company prioritized profit over safety.

Crash victims' family members attended both hearings, holding up photographs of their loved ones at times. Muilenburg said he hasn't offered his resignation. He repeatedly said that his upbringing on an Iowa farm taught him to see the problem through.

When Muilenburg repeated his background, a group of victims' relatives said "go back to to the farm" during the hearing, the mother of one of the crash victims told the CEO after the hearing. "It has come to the point where you are not the person anymore to solve the situation," the woman told Muilenburg.

In one of the biggest revelations of the House hearing, in 2015, more than a year before the planes were certified by federal regulators, a Boeing engineer asked whether a flight-control system that was involved in both deadly crashes was safe because it relied on a single sensor.

Regulators around the world banned airlines from flying the planes after the crashes. Boeing has changed the planes' system so that they rely on two sensors instead of one. But regulators have not yet signed off on that and other changes the company has made to the planes, leaving them grounded for nearly eight months, which has crimped airline profits.