Airlines using engines like the one that failed on a Southwest Airlines flight over Pennsylvania this week have 20 days to perform an inspection that could spot a flaw that likely led to the incident, federal authorities ordered Friday.

The emergency airworthiness directive from the Federal Aviation Administration was based on a proposal that had been pending since August 2017. Tuesday's engine failure that led to a passenger's death prompted the oversight agency to issue the emergency order, the document stated. FAA personnel were not available to comment Friday night.

Friday's order requires airlines using CFM56-7B series engines with more than 30,000 flight cycles to subject the engine's fan blades to ultrasonic inspection, a process using technology similar to an ultrasound that can detect flaws and stress in metal that are not visible to the naked eye.

A Southwest Boeing 737-700 flying from New York City to Dallas suffered an uncontained engine failure Tuesday that appears to have been caused by a broken fan blade in the engine turbine. The explosion blew debris into the plane's fuselage and shattered a window, causing a passenger to be partially blown out of the plane. The New Mexico woman later died of her injuries.

Another Southwest 737-700 that suffered a similar engine failure in 2016, forcing an emergency landing, had the same type of engine and also had a broken fan blade. The titanium fan blades involved with both incidents showed signs of metal fatigue, according to the National Transportation Safety Board, which is still investigating both incidents.

CFM56 series engines are among the most common in use by commercial airlines, and experts have said they are generally reliable. The engine is built by CFM International, a partnership between General Electric and Safran Aircraft Engines, a French company. CFM, which issued a warning about the possibility of flaws in the fan blades last year, reported that it has manufactured 30,000 of the engines. They are used by 550 operators worldwide.

The FAA directive is broader in scope than the proposal introduced last year. That proposal recommended ultrasonic inspections for engines with 15,000 flight cycles, or about four years of service, without a trip to a maintenance shop. That directive was anticipated to impact 220 engines, although in a comment responding to the FAA proposal Southwest said the number of engines that would need to be tested was well beyond that number, because it didn't track the wear on the individual fan blades in engines.

The emergency directive issued Friday did not state how many aircraft would be affected, but it did away with the earlier stipulation that considered how recently the engine had been in a maintenance shop.

Southwest did not immediately reply to request for comment.

Friday's directive requires one-time testing on all 24 fan blades in a CFM56 engine, but states the FAA may consider additional rule making. It also states the order does not apply to engines that have already undergone testing since CFM issued its first recommendation to conduct ultrasonic inspections in March 2017.