The FAA said the "emergency" order was based on a service bulletin, also issued Friday from the engine's manufacturer, CFM International, that called for more stringent testing of the CFM56-7B engine and an investigation into the deadly engine failure on Southwest Flight 1380, the airline regulator said.

It was the first accident-related passenger death on a U.S. airline since 2009 and the first passenger fatality due to an accident or incident in Southwest's history.

One passenger was killed after she was partially sucked through a window that was blown open in the blast when a fan blade on one of the Boeing 737's engines broke loose as the plane was flying above 30,000 feet. The plane, which was headed from New York to Dallas, made an emergency landing in Philadelphia.

The Federal Aviation Administration on Friday ordered airlines to inspect the fan blades of some engines of the same type that exploded on a Southwest Airlines flight earlier this week.

Under the FAA's order some engines will have to be inspected within 20 days.

The engine type is one of the most commonly used around the world. Friday's order will affect some 352 engines in the U.S. and 681 worldwide, said the FAA, citing the manufacturer's estimate.

"We are issuing this [airworthiness directive] because we evaluated all the relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of the same type design," said the FAA's notice.

CFM International, a joint venture of General Electric and France's Safran Aircraft Engines, said engine inspectors can examine the engine while it is still on the wing using an ultrasonic probe. Tiny cracks in the engine's fan blades may not be visible to the naked eye. That test takes about four hours per engine, CFM said.

CFM recommends ultrasonic inspections within the next 20 days to fan blades of CFM56-7B engines with more than 30,000 cycles, or uses, since new. Also, it recommends inspections by the end of August for fan blades with 20,000 cycles and inspections to all other fan blades when they reach 20,000 cycles.

After the first inspection, operators are recommended to repeat the inspection every 3,000 cycles, which typically represents about two years in airline service.

Southwest said its existing maintenance program "meets or exceeds all the requirements" in the FAA order.

Not all airlines will be subject to the order because it is based on the number of cycles of the engines. For example, a spokesman for American Airlines said its 737-800s that use the engines in the order haven't been used enough times to be subject to the order.

The FAA announced:

The Federal Aviation Administration (FAA) issued an Emergency Airworthiness Directive (EAD) that requires operators to inspect fan blades on certain CFM56-7B engines within 20 days. The directive is based on a CFM International Service Bulletin issued today and on information gathered from the investigation of Tuesday's Southwest Airlines engine failure. The inspection requirement applies to CFM56-7B engines. Specifically, engines with more than 30,000 total cycles from new must undergo inspections within 20 days. The EAD becomes effective upon publication. The engine manufacturer estimates today's corrective action affects 352 engines in the U.S. and 681 engines worldwide.

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