US aviation regulators have ordered inspections of Boeing 737 NG aircraft after cracks were found on some planes.
The Federal Aviation Administration (FAA) said Boeing discovered the cracks “while conducting modifications on a heavily used aircraft”.
Similar cracks were found in a small number of additional planes, the agency said.
Boeing said 737 NG operators have been contacted, but they have not reported any problems.
In its statement, the FAA said it would “instruct operators to conduct specific inspections, make any necessary repairs and to report their findings to the agency immediately”.