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Fan blades, engine cover are factors in Southwest flight 1380 engine failure



Preliminary data indicate an unexpected danger in the deadly flight and emergency landing of Southwest Flight 1380: the engine cover.

The

Southwest Airlines
Co.

Accident that killed a passenger Tuesday sent fast-moving debris into the left wing of the jet, outside the body of the aircraft and in the passenger cabin. Security experts are asking whether US regulators and engine manufacturers underestimated the role of engine cover in the unlikely event that engine parts erupt in mid-air.

A single rapidly rotating fan blade in the engine broke off as the aircraft crossed normally. apparently the result of the gradual weakening of the blade metal, the National Transportation Safety Board has said.

The cabin suddenly printed, and the plane snapped into a quick and steep, uninvited left-hander that would have frightened passengers, according to investigators. The pilots quickly reached wing height, but significant vibrations continued for the remainder of the flight, the investigators said.

The failure of the bucket and the resulting vibrations seem to have damaged the fairing or the outer cover of the engine, according to Alan Diehl, a former NTSB and Pentagon Air Crash Investigator. Parts of the fairing could have penetrated the hull and caused the worst damage, said Diehl. "The loss of a single vane inside the engine should not have such a dramatic impact," he said, referring to the separation of almost the entire engine hood and a nearby structure that directs air into the jet engine. Engine parts should not pass under the current manufacturing and inspection systems, which in the US and around the world are entering an era of Flight safety.

Depending on what investigators find, US and foreign regulators may mandate new or more frequent engine parts inspections

"I am very concerned about this particular event," NTSB Chairman

Robert Sumwalt

told reporters on Wednesday briefing. Note that this widespread family of

Boeing

The 737 engine has a solid safety record, saying it was too early to determine if the accident indicated a greater danger to the travelers. "If we feel that there is a deeper problem, we are in a position to make urgent safety recommendations," he said.

Historically, engine designers and inspectors were wary of internal parts that fired into the cabin engine. Kevlar shielding and other design elements are primarily intended to prevent such an event known as inconformed failure.

But experts tracking the probe are now focusing on an obvious vulnerability in disguise, which should not be affected by the type of internal error that apparently occurred on Tuesday.

Investigators have found numerous remains of cowling on the ground, including a large piece about 65 miles from where the aircraft was docked, Sumwalt said. "We're finding additional pieces," as more reports from the audience appear, he said.

Engine failures are rare, but are not unknown. Mr. Sumwalt said the investigators would see three or four incidents a year.

The CFM56-7B version, which participated in the Tuesday incident, has been in service since 1

997 and is used in more than 6,700 aircraft. European air safety supervisors said Wednesday they would look into the situation and work with US colleagues.

Ray Valeika,

a former maintenance and engineering chief at

Delta Airlines
Inc.,

The accident indicates that traditional approaches to risk reduction need to be adjusted. "To have a single hand, the disguise is so disturbing," he said.

Among the questions likely to be considered is whether Southwest has followed full recommendations for increased inspections by the engine manufacturer.

Investigators are expected Among other things, it should be investigated whether ultrasound examinations were carried out, as recommended in June 2017 by the engine manufacturer CFM International – a joint venture of

General Electric
Co.

and France

saffron
SA

, They try to determine whether the recommendations apply to the specific engine in the accident, to persons who are familiar with the details.

Such security bulletins are not binding, but airlines typically follow them carefully. In most cases, they are required by the Federal Aviation Administration.

Following an incident in 2016, CFM called on operators to carry out ultrasound tests on certain Boeing 737 engines to prevent fan blade tearing off due to metal fatigue. Later, the FAA suggested making such checks compulsory and having certain engines inspected within six months. This security policy is still pending, although one person who is familiar with the details said that the FAA was committed within weeks of the Tuesday's accident.

Now voluntary engine checks are being carried out in the southwest. However, both FAA and NTSB are required to examine Southwest's safety culture and dissect maintenance records to determine if the age and inspection history of the aircraft involved in the accident classify it in the non-binding inspection parameters. Tuesday's accident represents the first passenger deaths in Southwest's 51-year history, and the management was proud of its strong safety record.

As a longtime chairman

Herb Kelleher

In 2008 he retired and told well-wishers that his worst day had to do with a corporate jet that rolled at the end of a runway three years earlier, killing a child in a vehicle near Chicago's Midway Airport.

Gary Kelly,

The protégé of Mr. Kelleher and the manager of the carrier are now facing a similar test. He has undertaken to complete engine inspections quickly.

Mr. Kelly said that Southwest is still at an early stage of information gathering and cooperating with regulators and engine and aircraft manufacturers. He said that the aircraft involved in the Tuesday accident was last inspected on April 15, but did not include details of what maintenance was done.

Write to Andy Pasztor at andy.pasztor@wsj.com


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