The Federal Aviation Administration (FAA) said its order for engine inspections would be issued within the next two weeks.
It is something the FAA proposed making mandatory almost a year ago, but the draft directive was never approved.
Photos of the plane on the tarmac showed a missing window and a chunk gone from the left engine, including part of its cover.
Sumwalt said the fan blade, after suffering metal fatigue where it attached to the engine hub, suffered a second fracture about halfway along its length. European regulators recently implemented the same directive.
Southwest told the FAA in October that airlines needed 18 months and that only certain fan blades should be inspected, not all 24 in engines.
"Engine failures like this should not occur", Robert Sumwalt, chairman of the National Transportation Safety Board, said on Wednesday.More news: Morgan Stanley report: Next Indian govt may not enjoy a majority
The Southwest Airlines Flight 1380 incident appears to have involved an uncontained failure of the left engine that caused debris to strike the aircraft structure.
"The window had broken and the negative pressure had pulled her outside the plane partially", Peggy Phillips, a registered nurse who was on the plane, told WFAA-TV in Dallas. No plastic material from the window was found inside the plane.
One of the passengers on the flight, Marty Martinez, told CBS News about the incident while still on the aircraft.
NTSB investigators said passenger Jennifer Riordan was wearing her seatbelt when she was out a plane window that was shattered by debris. And you've probably ignored it 999 of those times - after all, you expect your plane to land safely. The flight data recorder showed the plane was at 32,500 feet when the engine failed about 20 minutes into the flight. CEO Gary Kelly said it had logged only 10,000 cycles since being overhauled.
Before Wednesday's announcement, critics accused the FAA of inaction in the face of a threat to safety. Boeing said it is providing technical help to the investigation, with which Southwest Airlines is cooperating.
Shults and Ellisor said they were focused on working with investigators and would not be speaking to the media.More news: Patriots' Tom Brady hasn't committed to playing in 2018, per report
Investigators said a blade that broke off mid-flight was showing signs of metal fatigue - microscopic cracks that can splinter open under the kind of stress placed on jetliners and their engines.
We are deeply saddened to confirm that there is one fatality resulting from this accident.
Marianne said the tragic situation would have been even worse for the family if Jennifer had been ejected from the plane.
The recommendation for more inspections followed an engine blowup on a 2016 Southwest flight. The NTSB said the probable cause of the wreck was "inadequate consideration" of "human factors" and "limitations in the inspection and quality control procedures used by United Airlines". A piece of the engine covering was later found in Bernville, Pa., about 112 kilometres west of Philadelphia, Sumwalt said.
Clearly, her death has affected quite a few people in her community.
So-called D checks are done roughly every six years for older planes, less frequently for newer ones. It can take weeks and involves taking apart much of the plane for inspection and possible fix or replacement of parts, then putting it back together. Engines are typically removed for work during a D check.More news: United Kingdom unemployment hits 40-year low
"They will begin to examine the inspection records for this engine and specifically for this fan section, these fan blades to understand the inspection history and what type of inspections were conducted", Sumwalt said.