Philadelphia - A Southwest Airlines Boeing 737-700 was forced to make an emergency landing in Philadelphia on April 17 after one of its engines had been severely damaged following the loss of a fan blade.

The Boeing 737-700, N772SW, with 144 passengers and five crew members on board took off from New York's LaGuardia airport for Dallas. After 20 minutes from the take-off, the Southwest's 737 lost its left engine at 32,500 feet, a CFM56, which sent a fire warning into the cockpit.

One of the 24 fan blades on the front of the engine was broken and damaged the entire engine through the air intake. Engine fragments penetrated the hull and damaged a cabin window, which also caused cabin pressure loss.

A female passenger seated at the window side was hit mortally in the head. Seven people were injured.

The cockpit crew shut down the damaged engine, initiated an emergency descent, and declared an emergency. The air traffic control gave the crew vectors for the Philadelphia International Airport, where the plane could land.

For landing, only the landing flap position 5 was selected, instead of the usual 30 or 40 degrees. After landing, the U.S. investigation authority NTSB (The U.S.) National Transportation Safety Board), was able to secure voice and data recorders and bring them to Washington D.C. for evaluation.

According to NTSB's initial investigation, material fatigue of the engine blade could have resulted in breakage. Southwest Airlines announced to control all engines of its Boeing 737s for material fatigue.

The final report of NTSB about the incident is expected in 12 to 15 months.

For Southwest Airlines, the uncontained explosion of a CFM56-7B engine on one of its Boeing 737-700s is not a first. The incident that occurred during the flight between New York and Dallas on April 17, 2018 was indeed preceded by another one that took place on August 27, 2016 during a flight between New Orleans and Orlando (Florida).

The debris generated by the explosion had damaged the fuselage, wing and empennage. The Boeing 737-700 for Southwest Airlines had then urgently landed at Pensacola airport, Florida.

The investigation had shown that a blade of the engine fan had separated from the fan. The analysis conducted by the NTSB experts then showed the existence of a "fatigue crack propagation."