Incident Overview

Date: Tuesday 17 April 2018
Aircraft Type: Boeing 737-7H4 (WL)
Owner/operator: Southwest Airlines
Registration Number: N772SW
Location: 105 km NW of Philadelphia, PA – ÿ United States of America
Phase of Flight: En route
Status: Substantial, written off
Casualties: Fatalities: 1 / Occupants: 149
Component Affected: Fan bladeFan blade
Investigating Agency: NTSBNTSB
Category: Accident
A Southwest Airlines Boeing 737-700, en route from New York-La Guardia Airport to Dallas-Love Field, experienced a significant incident at 11:04 near Philadelphia Airport. The aircraft’s no.1 engine suffered an uncontained failure, triggering a rapid and uncontrolled left roll. Due to the engine RPM dropping and oil pressure loss, the crew initiated emergency procedures, including a descent and a request for vectors to a suitable airport. The separation of the engine fan blade and cowling led to significant damage to the aircraft’s leading edge and a window breach, ultimately resulting in decompression and passenger fatality. The NTSB investigation revealed a low-cycle fatigue crack in the fan blade, which caused the fan blade to separate during flight, impacting the engine fan case and causing the critical fan cowl components to separate. This separation led to rapid depressurization and passenger fatality.A Southwest Airlines Boeing 737-700, en route from New York-La Guardia Airport to Dallas-Love Field, experienced a significant incident at 11:04 near Philadelphia Airport. The aircraft’s no.1 engine suffered an uncontained failure, triggering a rapid and uncontrolled left roll. Due to the engine RPM dropping and oil pressure loss, the crew initiated emergency procedures, including a descent and a request for vectors to a suitable airport. The separation of the engine fan blade and cowling led to significant damage to the aircraft’s leading edge and a window breach, ultimately resulting in decompression and passenger fatality. The NTSB investigation revealed a low-cycle fatigue crack in the fan blade, which caused the fan blade to separate during flight, impacting the engine fan case and causing the critical fan cowl components to separate. This separation led to rapid depressurization and passenger fatality.

Description

Southwest Airlines flight 1380 diverted to Philadelphia Airport, Pennsylvania, USA, after suffering an in-flight uncontained engine failure. The aircraft, a Boeing 737-700, originated from New York-La Guardia Airport at 10:43 for a flight to Dallas-Love Field, Texas. About 11:04, when the aircraft was climbing through FL325, the no.1 engine (CFM56-7B24) suffered an uncontained failure. The flight crew noticed that the no.1 engine rpm dropped to zero, as did the oil pressure. The cabin altitude horn sounded and the aircraft experienced a sudden, uncommanded, left roll of a 41ø bank angle. The pilots leveled the wing, donned their oxygen masks and initiated an emergency descent. The flight crew then requested air traffic control to give them vectors to the nearest suitable airport. As a result of the uncontained failure, a fan blade and parts of the engine cowling and engine air inlet cowl had separated. Debris impacted a window frame of row 14, causing the window and frame to break away. This resulted in a decompression of the aircraft. Additional debris impacted and damaged the leading edge of the left hand wing. The flight was vectored towards Philadelphia Airport, where the crew requested an extended final approach due to concerns of aircraft controllability. It was decided to land with flaps 5 for that reason, and an approach speed of 165 knots. The aircraft landed on runway 27L at 11:19 hours and the aircraft was stopped on a taxiway. ARFF services attended to the no.1 engine while injured passenger who was seated near the lost window was rushed to hospital. The passenger is reported to have died. Preliminary findings of the NTSB show that the no.13 fan blade of engine no.1 was missing. It appears to have broken away at the hub. There is evidence of metal fatigue in the area where the blade broke. Also, a part of the no.1 engine cowling was reported to have been found at Burnville, PA. Probable Cause: The National Transportation Safety Board (NTSB) determines that the probable cause of this accident was a low-cycle fatigue crack in the dovetail of fan blade No. 13, which resulted in the fan blade separating in flight and impacting the engine fan case at a location that was critical to the structural integrity and performance of the fan cowl structure. This impact led to the in-flight separation of fan cowl components, including the inboard fan cowl aft latch keeper, which struck the fuselage near a cabin window and caused the window to depart from the airplane, the cabin to rapidly depressurize, and the passenger fatality.

Primary Cause

Low-cycle fatigue crack in the dovetail of fan blade No. 13.Low-cycle fatigue crack in the dovetail of fan blade No. 13.

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