Investigators are probing fractures in a blade in Southwest engine failure

  • One person was killed Tuesday on a Dallas-bound Southwest flight after an engine exploded, the first fatality on a U.S. airline since 2009.
  • Airlines began inspecting some Boeing 737s after the incident.
  • Last August, the Federal Aviation Administration sought more rigorous testing of the engine involved, the CFM56-7B.

Federal investigators are probing the loss of a fan blade in a deadly Southwest engine failure.

One passenger was killed Tuesday on a Dallas-bound Southwest flight after an engine exploded, causing shrapnel to cut into the Boeing 737-700's fuselage, or the body of the plane. It blew out out a window and depressurized the cabin.

Passengers aboard Southwest Flight 1380 had rushed to pull the victim back into the plane after she was partially sucked out of a window, witnesses said. It was the first fatality on a U.S. airline since 2009.

The plane was climbing past 32,500 feet when indicators on the left engine started falling to zero and vibration significantly increased, said National Transportation Safety Board Chairman Robert Sumwalt. The cabin altitude warning started going off "shortly thereafter," which Sumwalt says usually occurs around 14,000 feet.

The plane made an unprompted roll on its left side at a 41 degree angle, he said, adding that rolls are rarely greater than 20 to 25 degrees. The plane made an emergency landing without using the usual amount of flaps, which help it slow down. It touched down at around 190 miles per hour, Sumwalt said, faster than the typical 155 miles per hour.

The entire event lasted twenty-two minutes, he said.

A missing fan blade appears to have cracked in two places, Sumwalt said. Investigators have evidence of an initial fatigue fracture on the inside of a blade near the hub that appears to have caused a second fracture about halfway down.

However, they only have part of the blade in their possession, Sumwalt said. Pieces of the outside part of the engine, knowing as cowling, have fallen to the ground in Pennyslvania.

Investigators found red paint marks on part of the left wing, indicating that some of the outside part of the engine, known as cowling, had broken off and hit it, Sumwalt said. They haven't found any acrylic, which the windows are made out of, inside the cabin, he said.

The engine involved, the CFM56-7B, is one of the most common in the world. All recent Boeing 737s are powered by engines from CFM International, a joint venture of General Electric and France's Safran Aircraft Engines.

However, it's too early to make any recommendations about the broader fleet of 737s, Sumwalt said.

"We are very concerned about this particular event," Sumwalt he at a press conference Wednesday. "Engine failures like this should not occur, obviously. And so yes, we're very concerned about this...To be able to extrapolate that to the entire 737 fleet, I will say if we find the need, if we feel this is a deeper issue, we have the capability to issue urgent safety recommendations."

Part of the NTSB's investigation will include determining how many and what type of inspections the engine, and particularly the section of fan blades in question, underwent, Sumwalt said.

The Federal Aviation Administration in August sought more rigorous testing of the engine involved, the CFM56-7B, one of the most common in the world. It proposed a rule that would subject the engines to ultrasonic tests of their fan blades.

Airlines began inspecting some Boeing 737 engines after Tuesday's incident.

Southwest late Tuesday said that it would accelerate testing of CFM56 engines "out of an abundance of caution" and that the ultrasonic checks of the engines' fan blades would likely be completed within 30 days. Several other airlines using this engine made similar announcements.

United Airlines CEO Oscar Munoz said in a quarterly earnings call Wednesday that the airline had started the inspections due to a service bulletin.

American Airlines began voluntary inspections of the engine's fan blades under the proposed federal guidance. The company said it continues to closely monitor the NTSB's investigation.

-CNBC's Leslie Josephs contributed to this report

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