The Federal Aviation Administration has ordered inspections of a Boeing 737 model after the company notified the agency of structural cracks.

Operators of certain 737 Next Generation planes will be required to make inspections, the FAA said.

“Boeing notified the agency of the matter after it discovered the cracks while conducting modifications on a heavily used aircraft. Subsequent inspections uncovered similar cracks in a small number of additional planes. The FAA will instruct operators to conduct specific inspections, make any necessary repairs and to report their findings to the agency immediately,” the agency said.

The cracking was found in the plane’s pickle forks, which attach the plane’s body to its wing structure, CNN affiliate KOMO reported.

Pickle forks are designed to last more than 90,000 landings and takeoffs without cracking, the affiliate said, and there could be dire results if the system fails, it said.

In a statement, Boeing said the “cracking issue” was found on a small number of airplanes.

“No in-service issues have been reported,” the company said. “Over the coming days, we will work closely with our customers to implement a recommended inspection plan for certain airplanes in the fleet. This issue does not affect any 737 MAX airplanes or the P-8 Poseidon.”

The Boeing 737 NGs are the models designated 737-700, 737-800, and 737-900.

Earlier this year, the FAA grounded all Boeing 737 Max planes after identifying similarities between two catastrophic crashes that left more than 300 people dead.

On Thursday, the National Transportation Safety Board released recommendations after an investigation into the certification of the 737 Max. The agency scrutinized the evaluation process for the Boeing 737 Max’s Maneuvering Characteristics Augmentation System (MCAS), a critical system at the center of both crashes.

Variances in pilot behavior are not being fully considered when the FAA evaluates an aircraft for certification, the safety board said.