Failure of Southwest Airlines Flight 1380 - Boeing 737-700, April 17, 2018

1. Incident Overview:

On April 17, 2018, Southwest Airlines Flight 1380, a Boeing 737-700 aircraft, experienced a catastrophic engine failure during a routine flight from New York's LaGuardia Airport (LGA) to Dallas Love Field Airport (DAL). The incident occurred approximately 20 minutes after takeoff, leading to an emergency landing at Philadelphia International Airport (PHL).

2. Initial Assessment:

The National Transportation Safety Board (NTSB) initiated an investigation to determine the root cause of the engine failure and assess any contributing factors. The primary focus was on the left engine, a CFM International CFM56-7B24.

3. Engine Component Analysis:

Detailed examination of the engine components was conducted to ascertain the cause of the failure:

a. Fan Blade Inspection:

• The investigation revealed that one of the fan blades had fractured, leading to a cascading series of events.
• Metallurgical analysis of the fractured blade indicated the presence of fatigue cracks.
• The cracks originated from the blade's interior and had progressed over time.

b. Fatigue Mechanism:

• The fan blade exhibited signs of low-cycle fatigue (LCF) and high-cycle fatigue (HCF).
• LCF was attributed to repeated stress cycles from takeoffs and landings, which had weakened the blade over time.
• HCF resulted from normal operational stress on the blade, leading to further propagation of the cracks.

4. Effects of Engine Failure:

The catastrophic engine failure had several significant effects on the aircraft's systems:

a. Debris Impact:

• Fragments of the dislodged fan blade struck the aircraft's fuselage, leading to a rupture and cabin depressurization.
• A window was shattered due to the debris impact, resulting in the expulsion of one passenger partially from the aircraft.

5. Crew Response:

The flight crew displayed exceptional professionalism and handled the emergency adeptly:

a. Rapid Descent and Emergency Landing:

• The flight crew declared an emergency and initiated a rapid descent to a lower altitude to provide passengers with breathable air.
• Effective communication and coordination among the crew ensured a safe and controlled landing at Philadelphia International Airport.

6. Findings and Probable Cause:

Based on the investigation, the following findings and probable cause were identified:

a. Findings:

• The engine failure was primarily caused by fatigue cracks in a fan blade, which resulted from a combination of low-cycle and high-cycle fatigue.
• Rapid decompression occurred due to the engine debris puncturing the aircraft's fuselage.

b. Probable Cause:

• The probable cause of the engine failure was attributed to the initiation and propagation of fatigue cracks in the fan blade, resulting in the blade's separation and subsequent damage to the aircraft.

7. Recommendations and Remedial Actions:

The investigation prompted several recommendations and corrective measures:

a. Enhanced Inspections:

• Regulatory authorities mandated more frequent and rigorous inspections of fan blades on similar CFM56-7B engines to detect fatigue cracks.

b. Engine Design Improvements:

• Engine manufacturers and airlines collaborated to enhance the design and materials of fan blades to mitigate the risk of fatigue-related failures.

8. Conclusion:

The failure of Southwest Airlines Flight 1380 highlighted the critical importance of continuous safety improvements and rigorous maintenance practices in the aviation industry. By investigating and addressing the root causes of incidents, the industry aims to enhance passenger safety and prevent similar occurrences in the future.