The planemaker in August identified a new quality problem with its popular 737 MAX aircraft involving supplier Spirit that resulted in improperly drilled holes on the aft pressure bulkhead made using an automated drill. Boeing has expanded inspections to include hand-drilled holes, according to trade publication The Air Current, which first reported the problem.

"We continue to take the time necessary to ensure each airplane meets our standards and regulatory requirements prior to ticketing and delivery," Boeing said in a statement.

The company declined to comment further on the scope of the latest issue or whether it will be able to meet its 737 delivery target of at least 400 jets in 2023, citing the quiet period before it announces its earnings on Oct. 25.

Boeing notified the Federal Aviation Administration of its initial findings earlier this week, along with customers already facing delivery delays of 737 Max 8s, according to The Air Current.

The FAA told Reuters it is "aware of the issue and are working it through our regular oversight process. There is no immediate safety concern."

Spirit said it continues working closely with Boeing to address rework related to the aft pressure bulkhead.

Boeing shares were down 1.8% in after-hours trading.

Deliveries of Boeing's best-selling 737 MAX fell in September to the lowest level since August 2021 as it continues struggling with work needed to correct the manufacturing defect.

In September, Boeing Chief Financial Officer Brian West said the company was still on track to meet the "low end" of its 400-450 jet target for annual 737 deliveries, despite the aft pressure bulkhead issue.

However, about 165 MAXs on Boeing's production line would need time-consuming x-ray inspections before being handed off to customers, he said.