Boeing's problems with its 787 Dreamliners continue. This time, the horizontal stabilizer in the Dreamliner's tail is raising concerns. There may be wider than allowable gaps between components in the stabilizer. Boeing's engineers discovered the problem after an internal audit earlier this year. It could impact up to 89% of the approximately 1,000 Dreamliners manufactured so far.

Tiny gaps could lead to premature aging

According to Boeing, parts of the horizontal stabilizer were clamped together incorrectly during assembly.

“... Certain components were clamped together during the build process with greater force than specified," a Boeing spokesperson was quoted saying in The Seattle Times.

This could cause gaps between parts in the stabilizer. These gaps could potentially be wider than the five-thousandths of an inch that’s allowable in the specifications. It could lead to premature aging.

“It is not an immediate safety of flight issue as none of the airplanes in service are within a window where they would begin to experience this aging,” said Boeing's spokesperson. The manufacturer recently produced its 1000th Dreamliner. The problem could affect nearly 900 of them.

Boeing will fix the problem on Dreamliners still at the factory. It is deciding whether Dreamliners already flying need to get pulled out of service and have modifications made.

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Boeing aware of the problem since February and self-reported to the FAA

The horizontal stabilizers were manufactured in Salt Lake City. Boeing engineers spotted the problem back in February. Boeing self-reported to the FAA. But it's only in the last week that senior FAA officials became aware of the problem.

The FAA is now investigating. The safety watchdog says its too early to talk about the nature or extent of any future airworthiness directives.

"We continue to engage with Boeing," the FAA said in a statement.

A series of problems to waylay production of Boeing's 787

The horizontal stabilizer flaw is the latest in a line of issues to waylay Boeing's Dreamliner production. The aircraft has proved a solid seller for Boeing. But its production has been beset with delays and quality control issues.

The problem with the horizontal stabilizers becomes the third active issue with the Dreamliner that Boeing is addressing. Within the past year, Boeing found two separate quality defects in the manufacture of the Dreamliner's aft fuselages.

In August 2019, Boeing identified a problem with the joining material (known as shims) used to fill gaps where parts of the fuselage were mated. The shims were too small. While the shims were within the acceptable margin for variation, some could rub up against roughness in the inner lining. Boeing has since fixed this.

FAA involved; may step up inspections

More recently, Boeing discovered further problems concerning the fuselage. A non-flat inner skin surface around some fuselage joins was too rough. Taken together, these two fuselage issues could weaken the carbon hulls and make the aircraft unable to fly safely in certain circumstances. That caused Boeing to ground eight Dreamliners in August, including aircraft flying for United Airlines, Singapore Airlines, and Air Canada. The Seattle Times quotes an unidentified FAA engineer saying;

“Grounding airplanes for manufacturing flaws is unprecedented and unbelievable.”

According to reports, multiple FAA investigations into the 787 Dreamliner are now a single, larger, investigation. While neither Boeing nor the FAA believes the latest problem to buffet the Dreamliners poses an immediate safety threat, the FAA is said to be looking at accelerated or enhanced inspections of hundreds of 787 Dreamliners.