NEW YORK (WABC) -- NTSB investigators are trying to figure out why a piece of an engine tore off during a Southwest Airlines flight that took off from LaGuardia, and broke the window of the Boeing 737 at 32,000 feet.
The plane made an emergency landing in Philadelphia.
The Eyewitness News Investigators have learned that the FAA proposed high-tech testing for metal fatigue on this type of airplane engine, but that proposal has still not been approved.
The potential metal fatigue problem with this model engine was on the FAA's radar.
So concerned that the safety agency wanted to mandate x-ray-type inspections of the fan blades on thousands of 737's with these engines.
But because of red tape or airline industry pressure, the FAA has been unable move the mandate beyond the proposal stage.
It didn't take long for NTSB investigators to zero in on what caused the mid-air engine failure:
Titanium blades on the left engine fan had broken off because of metal fatigue. In 2016, a broken fan blade separated from the same type of engine, also forcing the Southwest 737 to make an emergency landing.
Metal fatigue was cited as a factor and even prompted the FAA to draft a proposal to make mandatory ultrasonic inspection of fan blades on this type of engine.
The FAA had concluded the unsafe condition likely existed in other same model engines. The FAA was still waiting to finalize the proposal when Tuesday's engine failure killed a passenger:
"There really isn't an excuse for that kind of a delay when you have such an imperative safety problem in 2016 and now 2018," said pilot and aviation attorney Daniel Rose.
The engine manufacturer did issue a service bulletin last year to airlines recommending that they perform a one-time ultrasonic inspection on fan blades.
The bulletin is not mandatory and Southwest Airlines has yet to say if that inspection had been done on the plane and on their fleet of 700 737's with the CFM-56 engine. Southwest says it is now accelerating their inspections.
"They will begin to examine inspection records," said NTSB Chairman Robert Sumwalt.
In a new development, the NTSB Chairman says they found two metal fatigue fractures in the engine fan blade:
"It was in the interior part of the fan blade so not more than likely, certainly not detectable from looking at it on the outside," said Sumwalt.
That's why checking these fan blades require ultra-sonic inspections.
The NTSB Chairman says he's not ready to tie this incident to any systemic problem with the 737 fleet which numbers in the thousands. Robert Sumwalt said, "If we feel this is a deeper problem we have the capability to issue urgent safety recommendations."
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FAA proposal on high-tech testing for engine metal fatigue still not approved
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