An internal service for Boeing employees to raise safety and quality concerns has “exploded” this year, an executive claimed, after a whistleblower said he endured retaliation for speaking up.

The planemaker has come under intense scrutiny since a terrifying cabin panel blowout in January prompted fresh questions about the production of its bestselling commercial jet, the 737 Max.

But the Federal Aviation Administration is now investigating allegations by the Boeing engineer Sam Salehpour that the manufacturing giant took shortcuts to reduce production bottlenecks while making its 787 Dreamliner. He also raised issues about the production of the 777, another wide-body jet.

Salehpour, who has worked at Boeing for more than a decade, says he faced retaliation, including threats and exclusion from meetings, after raising concerns. He is due to give evidence at a Senate hearing on Wednesday.

In a briefing on Monday, Lisa Fahl, a vice-president at Boeing who previously oversaw quality on the 787 production line, told reporters that the number of employees using Speak Up – an online portal for workers to confidentially flag safety and quality concerns – had surged in recent months.

“We have exploded in the amount of Speak Ups that have come in, because we’re continually encouraging it,” Fahl said. Submissions to the service in January and February alone was equal “to an entire year last year”, she estimated.

A spokeswoman for Boeing added that submissions were up 500% on the year during the first quarter, after the company heavily promoted Speak Up following the incident aboard Alaska Airlines Flight 1282 from Portland, Oregon, earlier this year.

This is “what we want”, Fahl added, describing how Boeing had tried to make it easier for staff to use the system and make sure their messages were distributed to the right executives for review.

While the company claims retaliation against whistleblowers is “not tolerated”, Salehpour says this is what he faced before going public last week. He has claimed sections of the 787 Dreamliner’s fuselage could break apart midflight after thousands of trips, describing in interviews with the New York Times how sections had been been improperly fastened together.

Salehpour also described how he “literally saw people jumping on the pieces of the airplane to get them to align” during production of the 777.

“That’s not part of our process,” Fahl said on Monday, when asked to comment on the claim. Another Boeing executive, Steve Chisholm, its chief engineer for mechanical and structural engineering, added: “I would expect any employees who have seen other employees jumping up and down on panels to let us know.”

The pair detailed how extensive tests and inspections had left Boeing confident in the safety and durability of its 787 and 777 jets.

During testing of a damaged piece of fuselage, for example, Chisholm said 40,000 strikes by a controlled pendulum with a weight of over 300 pounds produced “no growth in the damage”.

After scrambling to reassure regulators, airlines and passengers in the wake of January’s blowout, Dave Calhoun, Boeing’s chief executive, and Larry Kellner, chairman of its board, announced plans to resign last month.