A Boeing 737 MAX 8 airplane rolls toward takeoff before a test flight at Boeing Field in Seattle. (AP Photo/Ted S. Warren, File)
INTERNATIONAL –The US Federal Aviation Administration (FAA) is ordering US aircraft operators to inspect 165 Boeing 737 Next Generation (NG) airplanes for structural cracks within seven days.

It came after Boeing notified the FAA that it discovered structural cracks on an aircraft undergoing modifications and similar cracks in some additional planes last month.

The NG is a precursor plane to the Boeing 737 MAX, which has been grounded since mid-March following two deadly crashes.

FAA said on Wednesday in a statement given to Xinhua that it requires operators to inspect aircraft with more than 30,000 cycles within seven days of the issuance of the rule.

Also, aircraft between 22,600 and 29,999 cycles must be inspected within 1,000 cycles, according to FAA. A cycle is defined as one pressurization and de-pressurization, typically corresponding to the number of flights.

The rule will affect 1,911 US-registered aircraft and approximately 165 aircraft must be inspected within seven days.

The inspections can be done visually and should require about an hour per airplane, according to the statement.

FAA said the cracks may "adversely affect the structural integrity of the airplane and result in loss of control of the airplane."

The new risks may strike another blow to Boeing as its 737 Max planes were grounded earlier this year following two deadly crashes.