Investigation Summary
The accident was triggered by the catastrophic failure of the 1st stage High Pressure Turbine (HPT) disk in the left (No. 1) Pratt & Whitney PW4090 engine. During the takeoff roll, the disk fractured due to low-cycle fatigue cracks that had originated from a machining defect, specifically a 'step' exceeding allowable limits, created during the manufacturing process. Fragments from the disk pierced the engine case, severing fuel and oil lines. While early investigative reports suggested low-pressure turbine involvement, the Japan Transport Safety Board (JTSB) final report confirmed the HPT disk as the source of the failure. The JTSB found that Korean Air's non-destructive testing (NDT) during maintenance had failed to detect the growing cracks. Furthermore, the emergency response was marred by crew errors: the pilots could not immediately locate the emergency checklist and ordered an evacuation before the engines had fully shut down, creating a hazard for passengers exiting near the intakes and exhaust. Passengers also complicated the evacuation by attempting to take carry-on luggage down the emergency slides.
Final Conclusions
The JTSB final report, released on July 26, 2018, concluded that the primary cause was the fracture of the HPT disk due to fatigue cracks initiated by a manufacturing machining error. Contributing factors included the failure of both the manufacturer's initial inspection and Korean Air's subsequent maintenance inspections to detect the defect. The report also cited the flight crew's failure to follow standard emergency procedures, specifically regarding engine shutdown before evacuation and the timely use of checklists.
Photographic Evidence (1)
Video Analysis
Hidden Failure | Korean Air Flight 2708 — An analysis of the uncontained engine failure and fire involving a Korean Air Boeing 777 at Haneda Airport in 2016.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
First Officer
Systems & Failure Modes
Pratt & Whitney PW4090 Engine
The left engine suffered an uncontained failure of the 1st stage High Pressure Turbine (HPT) disk due to fatigue cracking.
Fuel Oil Heat Exchanger
Impact forces from the disk failure caused cracks in this component's outer case, leading to the fuel and oil leaks that fueled the fire.
Emergency Evacuation Slides
Used for the rapid egress of 319 occupants; some were at risk of damage due to passengers carrying luggage against crew instructions.
Interesting Facts
- 01The aircraft was the 120th Boeing 777 produced, delivered to Korean Air in 1999.
- 02Fragments of the failed turbine disk were found scattered up to 600 meters from the start of the takeoff roll.
- 03The fire was caused by fuel and oil leaking from a cracked Fuel Oil Heat Exchanger case hitting hot engine parts.
- 04The evacuation was initiated before the engines were fully shut down, risking injury to passengers from jet blast or suction.
- 05The FAA issued an Airworthiness Directive for PW4000 series engines following the investigation's findings on the HPT disk.
- 06The aircraft was repaired and returned to service with Korean Air on June 3, 2016.
Safety Actions & Advisories
FAA Airworthiness Directive
The FAA mandated inspections of Pratt & Whitney PW4000 series engines to evaluate the condition of HPT disks and prevent similar fatigue-related failures.
Maintenance Inspection Review
Korean Air was advised to improve non-destructive testing (NDT) procedures to ensure small fatigue cracks in engine components are detected during routine overhauls.
Location
ACCIDENT SITE · Coordinates taken from the official investigation report.