GEOFF BENNETT: Boeing has faced intense scrutiny for months.

And, as our aviation correspondent, Miles O'Brien reports, new whistle-blower claims were the focus of a congressional hearing today.

SEN. RICHARD BLUMENTHAL (D-CT): Boeing is at a moment of reckoning.

It's a moment many years in the making.

It is a moment that results not from one incident or one flight or one plane or one plan.

MILES O'BRIEN: Lawmakers and whistle-blowers today slammed Boeing's safety culture, highlighting supply chain mismanagement, relentless production pressure, and allegations of other design errors that have besieged the company.

SAM SALEHPOUR, Boeing Whistle-Blower: I have analyzed Boeing's own data to conclude that the company is taking manufacturing shortcuts on the 787 program.

MILES O'BRIEN: Engineer Sam Salehpour is just the latest in a long line of Boeing whistle-blowers.

He told a Senate subcommittee he has serious safety concerns about the 787 Dreamliner, a fuel-efficient long-range wide body that is Boeing's newest design.

The alleged problem?

Pieces of the fuselage improperly joined together.

SAM SALEHPOUR: In a rush to address its bottlenecks in production, Boeing hit problems, pushing pieces together with excessive force to make them appear that the gaps don't exist, even though they exist.

The gap didn't actually go away, and this may result in premature fatigue failure.

Effectively, they are putting out defective airplanes.

MILES O'BRIEN: That said, the Federal Aviation Administration has taken no moves to ground the 787 and have not said they are unsafe.

In a statement today, Boeing dismissed Salehpour's claims and said: "Under FAA oversight, we have painstakingly inspected and reworked airplanes and improved production quality to meet exacting standards that are measured in the one-hundredths of an inch.

We are fully confident in the safety and durability of the 787 Dreamliner."

The company also denied any fatigue problems with the fuselages under repeated testing.

Boeing's public battering comes amid a series of harrowing fatal and near-fatal mishaps and accidents with its 737 airliners.

In January, an improperly installed door plug on a 737 MAX 9 blew off mid-flight, prompting the most recent round of public and regulatory scrutiny.

Boeing's safety nosedive first came to public light in 2018 and '19, when two 737 MAXes crashed, killing 346 people.

In the wake of those accidents, Boeing faced a criminal charge that it defrauded the FAA.

The company paid more than $2.5 billion to settle.

Ed Pierson, a former Boeing senior manager who left in 2018 and a whistle-blower himself, said little was learned.

ED PIERSON, Former Senior Manager, Boeing: The world is shocked to learn about Boeing's current production quality issues.

I'm not surprised, because nothing changed after the two crashes.

There was no accountability.

Not a single person from Boeing went to jail.

MILES O'BRIEN: Pierson feels the FAA policy that allows manufacturers to police themselves is also a key part of the problem.

ED PIERSON: The gold standard is now fool's gold, because the only thing that is more dangerous than a dangerous environment is the illusion of a safe environment.

MILES O'BRIEN: Salehpour's allegations land on a long, troubling list.

SAM SALEHPOUR: All the problems that we have had, we put Band-Aid over Band-Aid to resolve the problems, and Band-Aid over Band-Aid doesn't cover it.

MILES O'BRIEN: He says he and other whistle-blowers endured professional retaliation and threats after raising concerns internally.

SAM SALEHPOUR: You just try to escape from that, because this is hell that I was subjected to.

SEN. JOSH HAWLEY (R-MO): Yes.

Rather than saying, you know what, you have got a point, we need to maybe do something about this, they're telling you to hide it.

They're reassigning you.

They're threatening you.

SAM SALEHPOUR: Threaten you, sideline you, transfer you.

MILES O'BRIEN: In response, Boeing said retaliation is strictly prohibited.

But the company also said: "We know we have more work to do to foster a safety culture and we are taking action across our company to encourage all employees to raise their voice."

Senator Richard Blumenthal reiterated his invitation to Boeing CEO Dave Calhoun to testify at a later time.

Calhoun says he will step down by the end of the year.

For the "PBS NewsHour," I'm Miles O'Brien.