It also criticised the FAA, which certified the aircraft as safe to fly.
Seven whistleblowers from the sector provided testimony for the Senate Committee on Commerce, Science and Transportation.
It was in response to the deaths of 346 people in two Boeing 737 Max accidents.
Boeing stated that it was reviewing the report. "Boeing colleagues are encouraged to speak out whenever they have safety and quality concerns," said the planemaker.
The FAA also stated that the FAA had previously reported many of the issues in the report. Boeing is working to resolve them.
The FAA stated Monday that it takes all whistleblower claims seriously and will not tolerate retaliation for those who raise safety concerns. "Whistleblowers raised serious issues, but were ignored, or sidelined. Lives were at risk. It's a familiar refrain. However, some whistleblowers are now being listened to.
The Senate report is based upon testimony from seven individuals, all highly qualified. One of the two remains employed at Boeing while the other is at FAA.
These include Ed Pierson (a former senior manager on 737 Max); Martin Bickeboeller who played a key role in the development and launch of the 787; as well as Joe Jacobsen, a former FAA safety engineer.
Their testimony shows a worrying picture of inadequate safety oversight and lax production standards at a time when industry is facing new challenges due to increasing aircraft complexity.
Both Boeing and the FAA insist that they have addressed the flaws highlighted in the report. Two whistleblowers from the list told BBC that they had concerns about safety of the 737 Max.
The 97-page Aviation Safety Whistleblower Report alleged that the FAA's safety certification process was subject to undue pressure from line engineers and production personnel.
It also discussed conflicts of interest where, for example, the same engineer was responsible for preparing equipment and carrying out official tests.
According to the report, engineers with technical expertise were either ignored or marginalized during the development of the 737 Max and 787 Dreamliner.
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According to one instance, an FAA engineer alerted his superiors that there was a danger of the 787 suffering "catastrophic fire due to uncontrolled fire" because of the way the batteries were placed. Battery fires were the reason that 787 was grounded in 2013.
Whistleblowers also claim that the FAA's processes are flawed, which "have led to aircraft designs that don't meet the most recent standards of airworthiness".
This allowed the 737 Max, later implicated in both crashes, to be approved for flight while being equipped with software that had not been properly scrutinized.
The report stated that flaws in the aircraft's system were "creatively concealed or outright withheld from the FAA" during certification.
Further, the report stated that the FAA failed to have enough safety engineers to supervise the highly-criticized "Organization Designation Authorization" program, under which Boeing was responsible for a substantial amount of safety certification work on their own products on behalf of regulator.
This process has been compared to Boeing "marking its homework", according to critics.
In addition, the committee's report draws upon testimony that shows the FAA prioritized efficiency by delegating more work. As a result, its safety oversight has been diminished.
The document noted that the regulator had recently certified two aircraft - namely the 787 Max and the 737 Max – which were then grounded for safety reasons.
This led to the death of hundreds of people in the case of the 737 Max and cost Boeing more than $20bn (PS15.2bn).
Boeing reached a deferred prosecution deal with the US Justice Department in January. This agreement included $2.5bn of fines and compensation related to the 737 Max crash.