Boeing has identified a new production quality issue leading to improper shimming and gap verification between certain components in the 787’s horizontal stabilizer, further slowing deliveries as it performs special inspections to address imperfections in fuselage skins and shimming problems within some of the airplanes’ aft fuselages, the company confirmed Tuesday.

Boeing delivered four “thoroughly inspected” 787s in August after it discovered the failures to meet skin flattening specifications. “There are very tight tolerances for the flatness of the fuselage skin inner mold line, where the joint occurs," a Boeing spokeswoman told AIN. "Anything greater than five-thousandths of an inch, which is roughly the width of a human hair, is outside of engineering tolerance.”

A year earlier, Boeing found that technicians installed improperly sized shims between parts in the aft fuselage in a batch of airplanes delivered early in 2019. The spokeswoman explained that after identifying the skin flatness problem, “out of an abundance of caution” engineers looked at the batch of airplanes produced in early 2019 and found both conditions in eight airplanes, prompting the company to remove them from service.  

“So we identified the second issue and because of location, the team...went back to look at the airplanes produced in early 2019," she said. 

In the most recent discovery, Boeing found that mechanics clamped together certain components in the horizontal stabilizer with greater force than required by engineering specifications. The mistake could result in improper gap verification or shimming as workers assemble the component.

“Our engineering analysis has determined this is not an immediate safety of flight issue,” said the spokeswoman. “There is additional analysis happening. It’s possible that this condition may lead to premature aging of the part. None of the airplanes in service are within a window when they would begin to experience this aging.”

The latest acknowledgment by Boeing comes two days after the Wall Street Journal reported that unnamed sources told it the FAA had begun a review of the 787’s production processes. At press time the FAA hadn’t responded to AIN’s request for comment.