(CNN) The Federal Aviation Administration is mandating additional engine inspections in the wake of the deadly Southwest Airlines engine incident last month.

A new airworthiness directive will require airplane operators to perform inspections on General Electric's CFM56-7B engines by the end of August, followed by future periodic inspections.

The FAA said it is concerned engines like the one used on Southwest Flight 1380 could suffer a similar fate. It "determined the unsafe condition ... is likely to exist or develop in other products of the same type design."

The airworthiness directive calls for an ultrasonic inspection because the cracks and metal fatigue are not visible to the naked eye.

Shortly after the incident, the FAA issued an emergency airworthiness directive requiring inspections. The new permanent airworthiness directive lowers the threshold for the ultrasonic inspections, expanding the number of engines requiring inspections by about 2,500 to an estimated 3,716 engines on US planes.

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