Southwest Engine Fan Blade Showed Signs Of Metal Fatigue
The fan blade on the Southwest Airlines 737 engine that failed last month showed signs consistent with metal fatigue, the US NTSB said in an update on its accident investigation.
The National Transportation Safety Board said an ultrasonic inspection of the CFM56-7B engine’s damaged fan blade revealed fatigue fracture features. The blades had over 32,000 engine cycles since new and were last overhauled 10,712 cycles before the accident.
The NTSB’s inspection showed the engine failure had caused significant damage to the wing’s leading edge and a cabin window which was missing.
Flight attendants, who were moving through the aircraft cabin immediately after the incident, observed that a female passenger in row 14 was partially out of the hole in the fuselage where the window had been. The flight attendants and two male passengers were able to bring the passenger in, but she died of her injuries.
The flight crew requested an emergency landing and were diverted to Philadelphia. The report shows that the captain was planning a long final approach into the airport to make sure that all checklists were completed, but decided to shorten the approach when the pilots learned of passenger injuries.
Of the 144 passengers and five crew on board the flight, eight passengers received minor injuries in addition to the single fatality.
As a result of the incident, the US Federal Aviation Administration and the European Aviation Safety Agency issued emergency airworthiness directives on April 20 requiring operators to inspect fan blades on older CFM56-7B engines.
The FAA followed that up this week with a new directive extending the inspections of the engine type on the Southwest Boeing 737-700.