Investigation Summary
The accident was caused by the failure of fan blade No. 13 in the left CFM56-7B engine. The blade separated at the dovetail due to a low-cycle fatigue crack that had gone undetected during previous inspections. When the blade failed, it impacted the engine fan case at a critical location, generating a high-energy shock that the fan cowl structure could not withstand. This led to the separation of large cowl components, including the aft latch keeper. This specific fragment struck the fuselage near a cabin window, causing the window to fail completely. The resulting rapid decompression pulled a passenger partially out of the aircraft. Despite the severe structural damage to the wing, fuselage, and horizontal stabilizer, and the loss of engine power, the flight crew maintained control and executed a high-speed emergency descent to Philadelphia.
Final Conclusions
The NTSB determined the probable cause was a low-cycle fatigue crack in the dovetail of fan blade No. 13. This led to the blade's separation and subsequent impact with the engine fan case at a location critical to the structural integrity of the fan cowl. The resulting separation of cowl components caused a fragment to strike and break a cabin window, leading to rapid depressurization and a passenger fatality. The investigation also highlighted that the current certification testing for engine fan blade failures did not fully account for the structural effects of a blade out event on the nacelle and cowl components.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
The captain was a former Navy pilot with extensive experience.
First Officer
Systems & Failure Modes
CFM56-7B Engine
The high-bypass turbofan engine suffered a 'blade out' event when fan blade No. 13 separated at the dovetail.
Engine Nacelle and Fan Cowl
The structure surrounding the engine failed to contain the secondary effects of the blade failure, allowing debris to strike the fuselage.
Cabin Pressurization
The loss of a cabin window caused an immediate and rapid loss of cabin pressure, requiring the crew to use supplemental oxygen and descend.
Interesting Facts
- 01The aircraft was a Boeing 737-7H4 manufactured in 2000.
- 02The engine was a CFM International CFM56-7B turbofan.
- 03The fan blade failed due to a low-cycle fatigue crack in the dovetail region.
- 04The passenger fatality resulted from being partially ejected through a shattered window during rapid depressurization.
- 05There were 149 souls on board, consisting of 144 passengers and 5 crew members.
- 06Eight additional passengers received minor injuries during the event.
- 07The aircraft landed approximately 17 minutes after the engine failure occurred.
- 08Substantial damage was found on the left wing, fuselage, and left horizontal stabilizer.
Safety Actions & Advisories
Enhanced Fan Blade Inspections
The NTSB recommended that the FAA require more frequent and advanced ultrasonic inspections of CFM56-7B fan blade dovetails to detect fatigue cracks before they reach a critical size.
Nacelle Design Redesign
Recommendations were made to Boeing to redesign the fan cowl structure on 737 Next Generation aircraft to better withstand the loads generated by a fan blade failure.
Location
ACCIDENT SITE · Coordinates taken from the ntsb final report.