An emergency directive prompted by the Southwest Airlines engine failure that led to an emergency landing in Philadelphia last week means 681 jet engines worldwide must be inspected for signs of weakness in their fan blades, the Federal Aviation Administration said Monday.

The FAA order affects engines that have undergone at least 30,000 takeoff and landing cycles, including 352 in the United States owned by Southwest and other airlines, agency officials said.

Southwest has said it will go further, inspecting the fan blades of all engines like the one that failed last Tuesday, leading to the death of one passenger and the landing at Philadelphia International Airport.

The National Transportation Safety Board says a fan blade on Flight 1380 appears to have broken off due to metal fatigue, ultimately causing engine debris to penetrate the cabin.

Airline technicians have been using ultrasonic equipment to inspect all fan blades of the type used in that aircraft, in an engine type called the CFM56-7B. The airline says that from now on, it will inspect fan blades in its Boeing 737 fleet every 3,000 cycles. So far, the airline says, the inspections have resulted in the cancellation of fewer than 40 of its 4,000 flights each day.

The FAA originally proposed inspections of the fan blades in this type of engine in August 2017, after a fan-blade failure in another Southwest flight. At the time, Southwest officials warned that they would need extra time, as the airline might need to inspect older fan blades that were installed in newer engines not covered by the proposal. Fan blades are sometimes swapped in and out of engines for inspection and maintenance.

Asked if its new inspection order, issued Friday, could potentially overlook any older fan blades installed in newer engines, the agency responded: "The Emergency Airworthiness Directive is considered to be an interim action and was designed to address the engines posing the most immediate risk. We are prepared to issue necessary follow on directive(s) to expand inspections to include additional engines."