"Boeing has notified the FAA and been in contact with 737 NG operators about a cracking issue discovered on a small number of airplanes undergoing modifications," the airline manufacturer said in a statement Friday.
The cracks have been found in a part called a "pickle fork," which helps attach a plane's fuselage to its wing structure, reported Seattle ABC station KOMO. The part helps manage the forces between the wings and the jet's body.
A retired Boeing engineer told KOMO that "it's unusual to have a crack in the pickle fork."
"It's not designed to crack that way at all," the engineer added. "Period."
The FAA said Friday it will "instruct operators to conduct specific inspections, make any necessary repairs and to report their findings to the agency immediately."
The cracking issue does not affect any P-8 Poseidon airplanes, Boeing said, or 737 MAX model, which is currently grounded while engineers work to correct issues with the plane's automated flight control system, the airline manufacturer added.