Faced with accusations, Boeing is “confident” in the safety and durability of the 787.

US planemaker Boeing on Monday defended criticized safety practices on its production lines. The company said it was “confident in the safety and longevity of the 787 and 777” during a briefing with two senior engineers on Monday. They disputed allegations that about 1,400 Boeing planes had serious safety flaws.

Boeing has highlighted the extensive testing procedures these devices are subject to to confirm its “full confidence” in the 787. The defense comes two days before a sensitive congressional hearing into a launch engineer’s allegations relating specifically to the Dreamliner 787. It is titled ” The investigation into Boeing’s safety culture deficiencies: First-hand witness testimony is scheduled to appear before a Senate subcommittee in Washington on Wednesday.

In particular, it will be an opportunity to examine the allegations of whistleblower Sam Salehpour, a Boeing engineer. He said design and manufacturing defects in the 787 or Dreamliner and 777 fuselages could reduce the safety of these long-haul aircraft. He claimed he suffered retaliation for speaking out about what he considered poor safety practices at Boeing.

The hearing comes as regulators and politicians tighten their scrutiny of the plane maker following the near-disaster of the Jan. 5 Alaska Airlines flight. Then the 737 MAX lost a poorly sealed door mid-flight, leading to an emergency landing.

“No wear” noted during testing

Sam Salehpour’s allegations state that the 787 Dreamliner’s part gaps are much higher than standard, which “can ultimately lead to premature failure due to wear and tear without any warning.” A quality engineer says this could create unsafe conditions and even “potentially catastrophic accidents,” according to a formal federal complaint released by the whistleblower’s attorneys.

Steve Chisholm, chief engineer of Boeing Mechanical and Structural Engineering, told reporters gathered at the Charleston, South Carolina, plant and via video conference that “no wear was detected” during testing. “We weren’t surprised by the lack of wear results,” said Steve Chisholm, noting that the composite materials that make up the 787 were chosen because they don’t corrode like traditional metals.

Sam Salehpour, described by his lawyers as an experienced quality engineer at Boeing, criticized Boeing for taking a series of “shortcuts” that “allowed potentially defective installations to be installed in Boeing 787 fleets,” according to the FAA complaint.

Boeing is going through difficult times after several incidents. These are three of the four models of commercial aircraft currently produced by the American group that are officially the subject of an investigation by the American Aviation Regulatory Agency (FAA). US civil aviation regulators, which have been keeping a close eye on Boeing’s beloved 737 since January, are also investigating the 787 Dreamliner and the 777 whose structural integrity was called into question by this whistleblower.