By now the name Tammie Jo Shults is famous. The former Naval aviator and pilot of the Southwest Airlines Boeing 737 operating as Flight 1380 was called to action when a fan blade broke off from the big turbofan engine on the left side of the twinjet. The failure threw engine shards against the side of the plane causing a breach of the fuselage. The explosive depressurization partially pulled a belted passenger out of the hole created by the engine failure, resulting in her death. It was the first such fatality in more than a decade aboard a US Airline aircraft.
What wasn’t known in the immediate aftermath of the mishap was just how close to total disaster the flight came. Captain Shults has since made it clear. Because of the structural failure caused by the uncontained engine failure and the impact on the flyability of the 737, Shultz and her copilot Darren Ellisor struggled to fly the crippled airliner to its emergency destination of Philadelphia International Airport, at one point making a 270-degree turn, known as the long way around, in order to make a 90-degree heading change because the 737 could only be effectively turned in one direction.
Now the NTSB has released its final report on the accident and it’s not what investigators and armchair investigators initially thought, though it was close.
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The NTSB had determined that the engine came apart when a fan blade separated from the engine, blowing the engine cowling apart. In its report, the Board describes the engine failure. “The airplane was equipped with two CFM International CFM56-7B24 turbofan engines. The CFM56-7B engine has 24 fan blades installed in the fan disk. The left engine failure occurred when one of the fan blades fractured at its root (referred to as a fan-blade-out [FBO] event). The fan blade fractured due to a low-cycle fatigue crack that initiated in the dovetail (part of the blade root), which remained within a slot of the fan disk.”
Along with Southwest, engine maker CFM and Boeing, the FAA has already mandated a new type of inspection, an eddy current inspection (ECI) on top of the already required fluorescent penetrant inspection (FPI).
What came as a surprise was that it wasn’t, as initially suspected, a part of the engine fan that breached the fuselage and pressure vessel but a part of the engine cowling.
The discovery might sound like a minor distinction given the magnitude of the explosion, but it is not. In the wake of the finding, the NTSB has recommended that Boeing look into the design of the cowling and the fuselage to determine how to better protect against such mishaps in the future.