Continue Reading Below
Aircraft operators must inspect 165 of the airliners within seven days after the issue was found on a small number of planes, according to Reuters.
The FAA says the order covers a total of 1,911 U.S. registered planes with inspections taking an hour per plane.
Southwest Airlines confirmed Tuesday that two of their Boeing 737 NG planes have been grounded because of cracked critical equipment, according to KOMO News.
KOMO was first to report that inspectors found cracks in a critical part of an 737 NG known as the pickle fork.
A pickle fork is the part that helps attach a plane's fuselage to the wing.
Southwest Airlines, United Airlines and American Airlines are among carriers that fly the 737 NG.
Southwest said it has "developed a schedule to perform overnight inspections" and does not expect operational disruptions.
Aircraft with more than 30,000 cycles must be inspected within seven days, while planes between 22,600 and 29,999 cycles must be inspected within 1,000 cycles.