Airline supplier Spirit Aerosystems says it's aware of a quality issue involving elongated fastener holes on the aft pressure bulkhead on certain models of the 737 fuselage it produces.
The Wichita, Kansas-based company said because it uses multiple suppliers, only some units are impacted and it will continue to make unit deliveries to Boeing.
"Boeing has determined that there is no immediate safety of flight concern associated with this issue for the 737 fleet and that the in-service fleet may continue to operate," Spirit Aerosystems said in a statement.
Aircraft manufacturers have wrestled with supply issues in recent years. Spirit Aerosystems builds the fuselage for Boeing's 737 Max narrowbody jet and substantial sections of aircraft bodies in other of its models. The company builds components for Airbus aircraft as well.
In April Boeing cautioned that production and delivery of a "significant number" of its 737 Max planes could be delayed because of questions about Spirit Aerosystems' work on the fuselages.
All Max planes were grounded worldwide for nearly two years after a pair of deadly crashes, and production flaws halted deliveries of the larger 787 jetliner several times in the past three years.
Shares of Spirit Aerosystems Holdings Inc. dropped more than 6% before the market open on Thursday, while Arlington, Virginia-based Boeing Co.'s stock slipped nearly 2%.