Fatal Southwest plane incident: Engine showed signs of 'metal fatigue'

The investigation into a deadly engine failure on a Southwest jet is focusing on whether wear and tear caused a fan blade to snap off, triggering a catastrophic chain of events that killed a passenger and broke a string of eight years without a fatal accident involving a U.S. airliner.

From investigators' initial findings, the accident appears remarkably similar to a failure on another Southwest plane two years ago — an event that led the engine manufacturer and regulators to push for ultrasonic inspections of fan blades on engines like the one that blew apart nearly 10,000 metres over Pennsylvania on Tuesday.

When investigators from the National Transportation Safety Board examined the broken engine in Philadelphia just hours after it made an emergency landing, they immediately saw that one of the left engine's 24 fan blades was missing.

"This fan blade was broken right at the hub, and our preliminary examination of this was there is evidence of metal fatigue where the blade separated," said NTSB chairman Robert Sumwalt.

Metal fatigue is a weakening of metal from repeated use and involves microscopic cracks. It can occur in fan blades, the aluminum skin on most planes, or other metal parts.

Investigators will focus on whether the fan blade broke off at cruising speed — around 800 km/h — and started an "uncontained" engine failure that sent debris flying like shrapnel into the plane, where it broke a window.

A woman sitting near the window was sucked partially out of the plane before other passengers managed to pull her back in. She later died, and seven others suffered minor injuries.

The deceased was identified as Jennifer Riordan, a Wells Fargo bank executive and mother of two from Albuquerque, N.M. 

A piece of the engine covering was later found in Bernville, Pa., about 112 kilometres west of Philadelphia.

The pilots of the twin-engine Boeing 737 bound from New York to Dallas with 149 people aboard took it into a rapid descent and made an emergency landing in Philadelphia. Oxygen masks dropped from the ceiling and passengers said their prayers and braced for impact.

The NTSB investigation is expected to take 12 to 15 months. 

"There needs to be proper inspection mechanisms in place to check for this before there's a catastrophic event," said Sumwalt.

Engine a joint venture of GE, Safran SA

Southwest said Tuesday night that it would inspect similar engines in its fleet over the next 30 days.

European regulators this month began requiring an inspection by early next year of the CFM56 engine. The actions show there has been some concern, albeit non-urgent, about the engine, a workhorse of the global civil aviation fleet that has logged more than 350 million hours of safe travel, but was also being examined after a 2016 accident.

The CFM56 was produced by a joint venture of General Electric Co and France's Safran SA called CFM International and is one of the most common engines, paired with the world's most-sold plane, the Boeing 737.

In August 2016, a Southwest flight made a safe emergency landing in Pensacola, Fla., after a fan blade separated from the same type of engine, and debris ripped a foot-long hole above the left wing. The 2016 incident prompted the U.S. Federal Aviation Administration (FAA) to propose ultrasonic inspections of similar fan blades and their replacement should they fail the test.

The FAA had "determined the unsafe condition described previously is likely to exist or develop in other products of
the same type design," according to its proposal last year.

The European Aviation Safety Agency (EASA) issued an airworthiness directive last month requiring a one-time ultrasonic inspection of each affected fan blade on models of CFM56 engines within nine months of April 2. It said that CFM had sent a service bulletin recommending inspections, leading regulators to make the directive. EASA said the directive was issued after the failure of a fan blade on a CFM56 engine, which led to the uncontained release of debris.

It did not name the airline involved or the incident, but the service bulletin it referenced was the same as in the FAA proposal.

The FAA proposal estimated 220 engines on U.S. registered planes would be affected and that checks would require two hours of labour per inspection.

Passengers praised one of the pilots, Tammie Jo Shults, for her cool-headed handling of the emergency. The former navy pilot was at the controls for the landing. She also walked through the aisle and talked with passengers to ensure they were OK after the aircraft touched down.

"She has nerves of steel. That lady, I applaud her," said Alfred Tumlinson, of Corpus Christi, Texas. "I'm going to send her a Christmas card, I'm going to tell you that, with a gift certificate for getting me on the ground. She was awesome."

In a recording of conversations between the cockpit and air traffic controllers, an unidentified crew member reported there was a hole in the plane and "someone went out."

Southwest CEO Gary Kelly said there were no problems with the plane or its engine when it was inspected on Sunday.