The crisis enveloping Boeing has deepened with the release of hundreds of internal messages between employees working on the 737 Max aircraft, which boasted of deceiving safety regulators and said the plane had been “designed by clowns”.

US politicians investigating Boeing said the messages were deeply disturbing and showed “a coordinated effort to conceal information” about flaws in the aircraft, which was grounded last year after two fatal crashes.

The messages sent between 2015 and 2018 show unnamed employees discussing the potentially fatal implications of what they believed was substandard work on the 737 Max project.

In an exchange in 2018, one refers to “to the very very few of us on the program who are interested only in truth”, and asks: “Would you put your family on a MAX simulator trained aircraft? I wouldn’t.”

The other employee responded: “No.”

In instant messages sent in April 2017 complaining about the Max’s flight management technology, an employee wrote: “This airplane is designed by clowns who in turn are supervised by monkeys.” They referred to its “piss poor design” and urged: “Let’s just patch the leaky boat”.

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Referring to the Federal Aviation Authority, the US regulator that certified the plane as safe to fly, another message says: “I’ll be shocked if the FAA passes this turd.”

One employee said in 2018: “I still haven’t been forgiven by God for the covering up I did last year.”

Another boasted in 2015 of “Jedi mind tricking” a national aviation safety body by “making them feel stupid” for pushing for more training requirements, saying: “I should be given $1000 every time I take one of these calls, I save this company a sick amount of $$$$.” A key attraction of the 737 Max, which has received 5,000 orders from airlines but is currently grounded worldwide, was that carriers could use it without needing to put pilots on costly simulator programmes. Boeing has now agreed to put pilots through simulator training if the plane is returned to service.

Another message from November 2015 notes that regulators were likely to want simulator training for a particular type of cockpit alert. “We are going to push back very hard on this and will likely need support at the highest levels when it comes time for the final negotiation,” one employee wrote.

Boeing said the released messages were “completely unacceptable” and admittedthey raised questions about its interactions with the FAA.

A total of 346 people lost their lives in two 737 Max crashes in Indonesia in October 2018 and Ethiopia in March last year that investigators say were caused by a new element of its automated flight control system or MCAS. The system was designed to compensate for the fitting of heavier engines by ensuring that the nose of the plane would automatically turn down to avoid stalling. Instead, the system played a central role in the Lion Air crash in Indonesia, in which 189 people died, and the Ethiopian Airlines accident, in which 157 people died, by lurching into action shortly after the planes had taken off. The pilots were unable to regain control of the aircraft despite wrestling frantically with the controls.

Facebook Twitter Pinterest A Boeing 737 Max aircraft sits on the tarmac at Boeing’s 737 Max production facility in Renton, Washington, US. Photograph: Lindsey Wasson/Reuters

Boeing said it was committed to transparency with the regulator. The redacted messages released overnight were given in full to the FAA and to a congressional inquiry in December, but were made public late on Thursday.

Peter DeFazio, the House transport committee chairman, who has been investigating the Max, said the messages “paint a deeply disturbing picture of the lengths Boeing was apparently willing to go to in order to evade scrutiny from regulators, flight crews, and the flying public, even as its own employees were sounding alarms internally.

“They show a coordinated effort dating back to the earliest days of the 737 Max programme to conceal critical information from regulators and the public.”

The FAA said after its review of the documents “it determined that nothing in the submission pointed to any safety risks that were not already identified as part of the ongoing review of proposed modifications to the aircraft.

“Any potential safety deficiencies identified in the documents have been addressed. The tone and content of some of the language contained in the documents is disappointing.”

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Boeing said on Thursday it was confident “all of Boeing’s Max simulators are functioning effectively” after repeated testing since the messages were written. The company fired its chief executive, Dennis Muilenburg, in December. Its chairman, David Calhoun, will take on the role on 13 January.

Boeing said the communications “do not reflect the company we are and need to be, and they are completely unacceptable”. It also said it had made “significant changes as a company to enhance our safety processes and culture” and the staff concerned would face disciplinary action.

The messages include some from a former Boeing senior technical pilot, Mark Forkner, and another 737 chief technical pilot, Patrik Gustavsson. Boeing disclosed other messages from Forkner in October in which he said he might have unintentionally misled regulators and raised questions about a key safety system in testing.

Meanwhile, in a sign of the wider problems caused by the 737 Max scandal, US aircraft parts maker Spirit AeroSystems announced on Friday it is laying off 2,800 employees at its Wichita, Kansas, facility due to the grounding of the plane.