US Transportation Agency Asks Boeing To Fix Faulty Fan Blade Design On 737-700 Jet

WASHINGTON (UrduPoint News / Sputnik - 20th November, 2019) The US National Transportation Safety Board (NTSB) has recommended that Boeing to redesign the fan cowl structure on its 737-700 jets after an engine failure and emergency landing last year that led to the death of a passenger.

"This accident demonstrates that a fan blade can fail and release differently than that observed during engine certification testing and accounted for in airframe structural analyses," NTSB Chairman Robert Sumwalt said in a statement on Tuesday. "It is important to go beyond routine examination of fan blades; the structural integrity of the engine nacelle components for various airframe and engine combinations needs to be ensured."

The NTSB said it determined during a public board meeting held Tuesday that a fractured fan blade from a CFM International CFM-56-7B engine, powering a Southwest Airlines Boeing 737-700, led to the engine inlet and fan cowl separating and subsequently damaging the fuselage, resulting in a rapid cabin depressurization.

One passenger died and eight others suffered minor injuries during the April 17, 2018 incident, when the fractured fan blade impacted the fan case, causing fan cowl fragments to strike the airplane's fuselage near a cabin window. There were 144 passengers and five crew members aboard.

The NTSB said the window departed the airplane, and the cabin rapidly depressurized.

"The NTSB noted, as part of its probable cause, the accident occurred when portions of the fan cowl separated in flight after a fan blade, which had fractured due to a fatigue crack, impacted the engine fan case at a location that was critical to the structural integrity and performance of the fan cowl structure," the statement said.

It said the separated fan blade impacted the engine fan case and fractured into multiple fragments. Some of the fragments traveled forward of the engine and into the inlet. The impact of the separated fan blade with the fan case also imparted significant loads into the fan cowl through the radial restraint fitting, which is what caused the fan cowl to fail.

The accident happened after Southwest Airlines flight 1380 departed New York's LaGuardia Airport, bound for love Field, Dallas, Texas. The flight crew then conducted an emergency descent and diverted to Philadelphia International Airport.

The NTSB's recommendations for the Boeing 737-700 fan cowl redesign comes amid a crisis faced by the giant US plane maker on its safety record and conduct over the 737 Max jet series.