A government committee reviewing how the Federal Aviation Administration certifies new passenger planes for flight has determined that the system is safe and effective but small changes need to be made.

The committee was appointed by Transportation Secretary Elaine Chao in April after two deadly crashes involving Boeing's 737 Max. The crashes in Indonesia and Ethiopia killed 346 people.

The committee found in a report released Thursday that the FAA's system of delegating some inspections to aircraft manufacturers is effective and allows the U.S. industry to thrive.

But the findings conflict with legislators who are investigating the crashes. Last week Democratic leaders of the House Transportation Committee accused Boeing of deceiving regulators and said they will introduce legislation to strip the company of all or part of its authority to help approve its own aircraft as safe to fly.

Transportation Committee chairman Rep. Peter DeFazio, D-Ore., and Rep. Rick Larsen, D-Wash., were reacting to a batch of messages between Boeing employees that were released at the urging of lawmakers on Friday. The employees questioned the safety of the now-grounded Max, called the aircraft a "joke" and talked about how they concealed problems from regulators.

But the Special Committee to review the FAA's certification process wrote that the FAA certification process is "rigorous, robust and overseen by engineers, inspectors, test pilots and managers committed to the primacy of safety." The committee found that it took five years for the FAA to certify the Max.

It recommended that the system of delegating inspections to manufacturers should continue, and the FAA and industry should work together to address concerns about "potential undue pressure" on company employees designated to do inspections as planes work through the approval process.

Initially the FAA determined that 35 of 93 elements of the Max could be delegated to Boeing employees, with 58 supervised by the FAA. But the ratio of delegated tasks changed through the years "as the FAA's confidence in the aircraft design and related risk analyses evolved, including Boeing's ability to manage such elements."

In its report, the committee pointed out that it was not doing an investigation of the Max approval process. "The committee's approach was collaborative, not investigatory," the report said. "Its mandate was to collect and analyze information, not find fault."

The committee wrote that U.S. commercial aviation is a "model of safety efficiency and innovation across the world," safely handling about 44,000 flights per day all year. Since 1996, the U.S. air carrier fatality rate has dropped from 80.9 per 100 million passengers to 0.6 per 100 million in fiscal year 2019, the report said.

The report said that aviation safety experts it interviewed agreed that the FAA's decision to certify the Max as an update to previous generation 737s rather than a new type of aircraft didn't affect the Max's safety. "Each said a new TC (aircraft type certificate) would not have produced more rigorous scrutiny of the 737 Max 8 and would not have produced a safer airplane," the report said.

Investigators have implicated new automated flight control software called MCAS as a cause of the two deadly crashes. News reports and congressional investigations disclosed internal Boeing documents that revealed concern within the company about the software.

A faulty sensor caused the system to activate before the two disasters, pushing down the nose of both planes. Boeing had not told pilots about MCAS until after the Indonesian Lion Air crash, and regulators at the FAA didn't know much about it either.

The House Transportation Committee disclosed an internal FAA analysis made after the first crash, which estimated that there would be 15 more fatal crashes over 45 years until Boeing fixed MCAS. Yet the FAA did not ground the plane until after the second crash.

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Krisher reported from Detroit.