Investigators reveal what caused window to shatter on fatal Southwest Airlines flight

• Southwest Airlines Flight 1380 suffered a catastrophic engine failure and cabin depressurization on April 17.
• The National Transportation Safety Board confirmed on Thursday that the cabin depressurization was caused by pieces of the engine cowling and inlet puncturing a window when the engine exploded.
• The exploding engine also caused damage to the Boeing 737-700's left wing and left horizontal stabilizer.

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The National Transportation Safety Board confirmed on Thursday what caused the window blowout onboard Southwest Airlines Flight 1380 last month.

According to investigators, the window in row 14 was punctured by pieces of the engine inlet and cowling that exploded after a fan blade in the left engine snapped off.

The punctured window caused the cabin of the Boeing 737-700 to depressurize, nearly sucking passenger Jennifer Riordan out of the aircraft. Riordan, 43, was pulled back into the plane by fellow passengers, but would later die from her injuries.

The exploding engine also caused heavy damage to the plane's left wing and left horizontal stabilizer.

On April 17, Southwest Airlines Flight 1380 was en route from New York's LaGuardia Airport to Dallas Love Field when it suffered the engine failure over Eastern Pennsylvania. The flight diverted to Philadelphia International Airport.

The NTSB announced hours after the incident that a preliminary examination of the failed engine showed signs of metal fatigue at the point where the blade broke off. Thursday's update confirms the initial diagnosis that blade number 13 of 24 failed due to metal fatigue.

No cracks were found in any of the engine's other fan blades.

The engine in question, the CFM56-7B turbofan, is the product of a 40-year-old joint venture between GE Aviation and France's Safran Aircraft Engines, called CFM International.

The CFM56 is arguably the most popular jet engine in the world with more than 30,000 units produced since 1980, and it's used on both civilian and military aircraft. The CFM56-7B debuted in 1997 and currently powers more than 6,700 planes in the world. CFM International is the exclusive engine supplier for the Boeing 737.

After the fatal flight, Southwest Airlines announced it is inspecting its entire fleet of more than 700 CFM-powered 737s for metal fatigue using ultrasonic sensors.

In addition, the engine's manufacturer and the Federal Aviation Administration have both issued alerts that called for older CFM56-7B engines to be immediately inspected.

Read more about the Southwest incident:

• Here's what happened on the fatal Southwest Airlines flight
• Southwest passenger's death was the first in a US passenger airline accident in more than 9 years
• Southwest pilot to air traffic control before emergency landing: 'There's a hole and someone went out'
• Southwest passenger says there was 'blood everywhere' after 'terrifying' emergency landing
• Southwest passenger who died after major engine failure has been identified as a Wells Fargo VP and mother of two
• Investigators found a major clue to what may have caused Southwest jet's engine failure
• The type of engine that blew apart on Southwest plane was a growing concern for regulators
• The pilot who made the Southwest flight emergency landing is a former fighter pilot and one of the first women to fly an F-18
• Southwest passenger's torso was sucked out of plane after engine explosion busted open aircraft window
• Southwest reportedly gives passengers who were on fatal flight $5,000 check and a $1,000 travel voucher

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