(CNN) The design of an engine fan blade that snapped on a Southwest flight in April, breaking an airplane window and partially sucking a woman out of it, has been a concern since the engine's earliest days, the manufacturer told investigators at a hearing Wednesday.
The hearing before the National Transportation Safety Board and an NTSB report also revealed frightening new details about the chaotic scene aboard Flight 1380, when pilots heard a loud bang, wind roared into the cabin through the broken window and oxygen masks dropped from the ceiling.
Jennifer Riordan, the passenger whose head and torso were sucked out of the plane, later died of blunt force trauma, according to a lengthy fact-finding report that will be the basis for the NTSB's eventual findings about the accident.
The Boeing 737 was headed from New York to Dallas on April 17 when the engine failed. NTSB investigators hope the hearing will help them pinpoint the cause of the problem and prevent the catastrophic events from happening again.
Investigators have zeroed in on the engine design and its history, which includes various design changes to address cracking and a 2016 engine failure involving another Southwest Airlines plane.
Engine manufacturer CFM International said at the hearing their CFM56-7B model failed its first certification test in the mid-1990s but ultimately passed a second certification test. Since then, engineers have made various design changes to prevent fan blade failures.
After the engines were put into fleet service, "some of those early engines, when we looked at the fan blades, it indicated the coating system was not staying intact as well as we had anticipated with the design change," said Mark Habedank, engineering leader for the CFM56 engine.
The company made a design modification, installing a piece of metal it called a "shim," and adding lubrication.
More recently, inspectors discovered similar cracked blades in the same engine model installed on other airlines' planes, Habedank said.
After the 2016 failure, CFM told operators to perform additional inspections of the fan blades.
Southwest, whose entire fleet is Boeing 737s, said the particular fan blade that failed had not met the requirements for additional scrutiny.
"At the time of the event, we had already inspected 603 engines," said Mark Wibben, an engineering manager at the airline. However, he said, "We had no basis to prioritize these fan blades versus any other blades in our fleet."
The failed engine's last maintenance work was performed in June 2017, the NTSB reported. It was manufactured in 1997 and overhauled in 2012.
CFM International is a joint venture between GE Aviation and Safran Aircraft Engines.
In a statement sent Wednesday to CNN, GE Aviation said that CFM "responded aggressively" after the 2016 incident and worked closely with regulators to inspect some 350,000 fan blades in the CFM56-7B fleet. All the fan blades were cleared by mid-August 2018, the statement said.
Interviews by the NTSB reveal new details about the frightening scene aboard the plane, which was carrying 144 passengers, three flight attendants and two pilots.
The first indication of a problem was a loud bang at 11:03 a.m, about a half hour after the plane took off from LaGuardia airport. The plane was flying at 32,000 feet when it banked steeply to the left and the oxygen masks dropped from the ceiling.
While alarms sounded in the cockpit, the pilots struggled with equipment issues that prevented them from communicating with flight attendants, air traffic controllers, firefighters and each other, while also recovering from the steep turn and figuring out where they could land.
In the cockpit, the pilots worked to level out the plane and began descending. But they told investigators that while wearing their oxygen masks, they couldn't speak to each other.
After finding the correct microphone switches, the pilots mistakenly believed the plane was on fire and asked an air traffic controller to route them to the Philadelphia airport.
"We're single engine descending have a fire in number one," one of the pilots said, according to the NTSB report.
At that point -- 11 minutes after the bang -- one of the pilots called back to the cabin to speak to the flight attendants. That was when the flight-deck crew first learned of the situation in the cabin, including an injured passenger, the NTSB report says.
The flight attendants were preparing to serve drinks when they heard the bang.
One flight attendant said that "because of the pressure in her ears, she could barely hear anything, the cabin was loud and windy," the report said.
A flight attendant discovered the harrowing scene in Row 14.
Riordan, who was sitting in a window seat by the wing, "had been pulled outside the airplane through the window," the report said.
The flight attendant "grabbed onto the passenger and tried to bring them back into the airplane with assistance from [another flight attendant]." Two male passengers helped and were eventually able to get the passenger back into the plane, the report said.
A nearby nurse and another passenger performed CPR on Riordan as the plane landed. One of the flight attendants did not make it back to her seat in time for landing, "so she sat on the aisle floor near row 4 or 5 and passengers held her down" as the plane touched down in Philadelphia, the report said.
The communications problems continued after landing. One of the pilots described "difficulty communicating with fire trucks on the radio and said the captain requested a discreet frequency." A pilot "eventually yelled ... to the fire chief from the forward entry door," the report says.
Riordan's family thanked the NTSB "for their very important work" in a statement on Wednesday.
"The most important thing now is making sure that the aircraft and engine failures that caused Jennifer's untimely and unnecessary death never happen again," the statement said.
Eight passengers who survived the Southwest Airlines flight filed a lawsuit in June against the airline, GE Aviation Systems, Boeing, Safran USA and CFM International. The defendants declined to comment at the time on the pending litigation.