In the latest issue, Boeing learned during fabrication of the 787 horizontal stabilizer that some components were clamped with greater force than specified, which could result in improper gap verification and shimming. Boeing identified the problem in February and announced it on Tuesday.
The Federal Aviation Administration (FAA) said Tuesday it "is investigating manufacturing flaws affecting certain Boeing 787 jetliners. The agency continues to engage with Boeing."
A person briefed on the matter said the horizontal stabilizer issue could require the inspection of as many as about 900 airplanes.
Boeing said the stabilizer issue, identified at a production plant in Salt Lake City, Utah, was being corrected on airplanes not yet delivered and was not an immediate flight safety issue.
"Analysis is underway to determine if action is required on the in-service fleet," Boeing added.
Boeing shares fell 5.8% Tuesday.
On Monday, the FAA said it was also investigating two other manufacturing flaws in some Boeing 787 Dreamliners, but said it was too early to say if it will require new inspections.
Boeing said in late August that airlines had removed eight 787 Dreamliners from service as a result of two distinct manufacturing issues in fuselage sections.
Boeing said Monday some airplanes have shims that are not the proper size, and some airplanes have areas that do not meet skin flatness specifications. Boeing identified the shimming issue in August 2019.
"Individually these issues, while not up to specifications, still meet limit load conditions. When combined in the same location however, they result in a condition that does not meet limit load requirements," Boeing said.
Boeing said Tuesday it expects the inspections will affect the timing of 787 deliveries in the near-term.
Boeing also said Tuesday it secured its first 737 MAX order in 2020, while also recording more cancellations as customers continued to ditch orders for the grounded MAX jets.
Boeing said it lost another 17 orders for the 737 MAX jet in August, bringing the total number of cancelled orders, including those where buyers converted the MAX to a different model, to 445 for this year.
Boeing delivered 13 aircraft in August, down from 18 planes a year earlier and up from four in July.