Southwest's White-Knuckle Ride in Focus as NTSB Probes Engine

(Bloomberg) -- Passengers aboard a crippled Southwest Airlines Co. jetliner endured a tense, bumpy, 22-minute ride after an engine failed and hurled a hail of shrapnel that blew out a window, causing the death of a woman.

The plane banked hard to the left by 41 degrees moments after the engine shut
down and its smooth exterior tore loose, dramatically increasing wind drag, said
National Transportation Safety Board Chairman Robert Sumwalt. That’s about twice the maximum bank that a traveler is likely to experience on a typical flight, he said at a briefing in Philadelphia on Wednesday.

Southwest's White-Knuckle Ride in Focus as NTSB Probes Engine

Pilots on Flight 1380 from New York to Dallas were able to level the aircraft quickly, but its damaged wing and engine cover created high vibrations for the rest of the flight, which ended with an emergency landing in Philadelphia. Jennifer Riordan, a passenger who had been seated near a window, was partly sucked out of the plane before passengers pulled her back in.

Philadelphia’s medical examiner found that she died of blunt impact trauma to her head, neck and torso, the Associated Press reported.

Southwest's White-Knuckle Ride in Focus as NTSB Probes Engine

Investigators are studying every moment of the brief flight, along with the maintenance history of the engines that powered the 17-year-old Boeing Co. 737-700 aircraft. Early indications point to metal fatigue where a fan blade on the afflicted engine had snapped off.

“We are very concerned about this particular event,’’ Sumwalt said. “Engine failures like this should not occur obviously.’’

Southwest is stepping up engine inspections as it grapples with its first accident to result in a passenger’s death. Examinations of the fan blades on its CFM56-7B engines will be completed within 30 days, the Dallas-based company said. The discount airline operates the world’s largest fleet of 737 jetliners, relying on the turbofan to power most of its more than 700 planes.

FAA Directive

The Federal Aviation Administration said late Wednesday that it would issue an airworthiness directive for the CFM engine within the next two weeks. The directive will require “an ultrasonic inspection of fan blades when they reach a certain number of takeoffs and landings. Any blades that fail the inspection will have to be replaced,” the FAA said. The directive finalizes actions the agency originally proposed last August.

The NTSB probe hasn’t uncovered any systemic issue with Southwest aircraft or planes at other airlines that requires immediate action, Sumwalt said. The NTSB has the power to move quickly to raise alarms if such problems are found, he said.

Investigators haven’t determined whether the engine that exploded had any special inspections following a separate incident on a Southwest airplane cruising over the Gulf of Mexico in 2016, according to Sumwalt.

On that plane, also a 737-700, a fan blade on a jet engine snapped off and sent debris slamming into the fuselage, safety-board investigators determined. They found evidence of a crack “consistent” with metal fatigue in the titanium-alloy blade. The jet was forced to make an emergency landing in Pensacola, Florida, after the plane lost cabin pressure and passengers tweeted pictures of themselves with oxygen masks on.

Airline Inspections

Regulators last year recommended an ultrasonic inspection of fan blades in CFM56-7B turbofans, while CFM issued bulletins to its operators outlining testing that’s needed.

Inspections of about 690 engines are “well underway,” United Continental Holdings Inc. said Wednesday. American Airlines Group Inc. already finished inspecting its 304 Boeing 737-800s with the same engine type, a spokesman said. Delta Air Lines Inc. said it “will take appropriate action as this ongoing investigation continues.”

Southwest completed inspections of its CFM56-7B engines earlier, and was partway through its own program to check the turbines on all of its 737-700s and -800s when the accident occurred, said spokeswoman Brandy King. Those reviews have been accelerated, she added. The carrier is not doing inspections on its new 737 Max airplanes equipped with the upgraded Leap engine, also made by CFM.

The CFM56 series turbofan, one of the most widely used jet engines and the sole engine for Boeing’s 737 New Generation family, has amassed more than 350 million flight hours on 6,700 aircraft since entering the market in 1997.

‘Premature’ Link

There have been “only a handful” of failures with the engine, Southwest Chief Executive Officer Gary Kelly told reporters late Tuesday. He said it would be “premature to link it to other engine failures that have occurred.”

While the average length of Southwest’s flights has increased as it has grown into the No. 4 U.S. carrier, the company is still known for its shorter, domestic flights and rigorous use of aircraft. The relatively high number of takeoffs and landings puts added stress on planes and engines.

“Anytime you run an engine like that to maximum power and hold it there for a couple of minutes on takeoff, you are putting maximum stress on all the rotating parts,” said John Nance, a former airline and military pilot. “You can’t deny that the more you run an engine up to full power on takeoff, the more you stress those blades.”

The strain those operations put on the aluminum frames of Southwest’s 737 jetliners has been raised before, notably after an aircraft’s roof tore mid-flight in 2011. The metal fatigue was later linked to the technique Boeing workers used to assemble the so-called 737 Classics aircraft family, which Southwest retired last year.

Metal fatigue was also blamed for a hole that opened atop a Southwest 737-300 in 2009, depressurizing the cabin and forcing an emergency landing. No one was injured. That episode prompted regulators to require checks on 135 Boeing 737-300s, -400s and -500s in the U.S.

In March 2009, Southwest agreed to pay a $7.5 million fine for flying jets in 2006 and 2007 without some required fuselage inspections. It was the FAA’s largest fine against an airline at the time.

Modern jet engines contain a series of spinning fans and if one of the blades breaks it can eject metal debris at high speeds. Engine manufacturers and airlines conduct periodic inspections on planes designed to spot any evidence of cracks or weakening of the metal because of fatigue.

After the latest accident, Kelly said Southwest would work “with the NTSB to make sure we understand the root cause, and any further actions we need to take in terms of maintenance or inspections we’ll want to add to our program.”

The incident is unusual for the destruction caused by the broken fan blade, despite the engine’s protective Kevlar casing, said Hans Weber, an aviation consultant. Also puzzling is how signs of fatigue might have been missed in a prominent, forward-facing engine part among the easiest for mechanics to inspect.

At his press briefing on Wednesday, however, Sumwalt said that a crack on a fan blade was on an internal surface that would not have been detectable by a visual inspection.

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