The FAA has issued an emergency directive requiring all airlines to inspect fan blades on their older CFM56-7B engines within 20 days.

The agency issued the airworthiness directive Friday night in the wake of last week's Southwest Airlines fatality that was caused by a fan blade that broke loose from a CFM56 engine due to metal fatigue.

Specifically, the directive says that airlines must conduct ultrasonic inspections on all blades of CFM56 engines that have been used more than 30,000 times.

Engine manufacturer CFM International, a joint venture between GE Aviation and France-based Safran Aircraft Engines, estimates that the directive impacts 352 engines in the U.S. and 681 engines worldwide, the FAA said.

The emergency order isn't as broad as a separate directive that the FAA also plans to issue in the next nine days. That directive is to require ultrasonic inspections of all CFM56 fan blades when they reach a designated number of takeoffs and landings.

Meanwhile, Southwest is moving quickly forward with its promise to conduct ultrasonic inspections of all its CFM56 fan blades within a month of last week's fatality.

Doing so, however, is coming at a cost to operations. The airline said Sunday that has been cancelling roughly 1% of flights in order to conduct the inspections.

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