A final report by the US House of Representatives on the crashes of two Boeing 737-Max planes confirmed that both the aircraft manufacturer and the US aviation authority FAA had serious errors.
The group and the agency had "repeated and serious failures," according to a report published by the Democrats from the responsible committee for transport and infrastructure.
The committee investigated the background of the two crashes with a total of 346 fatalities for 18 months.
"The Max crashes were not the result of a single failure, technical error, or poorly handled event," states the 245-page document.
"It was the terrible culmination of a series of false technical assumptions by Boeing engineers, a lack of management transparency and grossly inadequate oversight by the FAA."
Boeing is again accused in the report of a "culture of secrecy".
In the course of this, the aircraft manufacturer withheld important information from the authorities.
In addition, there was internal pressure at Boeing to get the 737 Max machines up and running as quickly as possible in order to be able to compete with the European competitor Airbus.
At the FAA, in turn, there was undue influence from high-ranking employees.
A flight ban continues to apply to 737 Max machines
The report contained "disturbing revelations about how Boeing - under pressure to compete with Airbus and provide WallStreet with profits - withheld critical information from pilots and ultimately put planes into service that killed 346 innocent people," said the committee chairman Peter DeFazio.
He is particularly angry "how Boeing and the FAA have put public safety at risk in the critical phase between the two crashes," said the Democratic politician from the western coast state of Oregon.
The allegations against Boeing are not new and were already raised in March in the preliminary final report, but they have now been substantiated with further evidence and formulated even more drastically.
Several Republican politicians have described the report to the US media as partisan and excessive.
Boeing's 737 Max is currently subject to a worldwide flight ban.
It was imposed in March 2019 after two planes of the type crashed in Indonesia and Ethiopia.
The US group points out that since then numerous changes have been made to the software, among other things.
At the beginning of July, the 737 Max had successfully completed a series of test flights that were intended to enable a new registration.