What happened
On June 7, 2016, a Biman Bangladesh Airlines Boeing 777-300ER, registration S2-AFP, was performing a commercial passenger flight from Hazrat Shah Jalal International Airport in Dhaka to Dammam, Saudi Arabia. During the takeoff roll, as the aircraft reached approximately 150 knots, an "ENGINE FAIL" warning appeared on the primary flight display, accompanied by master and aural warnings.
The flight crew immediately initiated an aborted takeoff procedure at an indicated airspeed of 149 knots. The aircraft successfully came to a stop on the runway. Following the stop, the crew communicated the engine problem to Air Traffic Control (ATC) and taxied back to the apron, eventually shutting down the engines.
Upon inspection by ground engineers, the right engine showed significant damage. A visual examination revealed severe damage to the rear part of the engine turbine section. Additionally, runway inspections uncovered hundreds of pieces of metallic debris, weighing approximately 13.56 kg, scattered on the runway surface.
The investigation
The Aircraft Accident Investigation Group of Bangladesh (AAIG-BD) conducted an investigation into the incident. Investigators performed borescope inspections of the engine, which revealed severe airfoil damage in the low-pressure turbine (LPT) stages. Specifically, investigators found that thermal degradation had occurred at the high-pressure turbine (HPT) stage 2 stator and affected the LPT stage 1 stator, with some airfoils appearing molten.
Further analysis of the engine hardware indicated that this thermal damage was followed by secondary mechanical damage caused by the conflict of rotating and static engine parts. The investigation focused on identifying the source of the extreme heat. Testing of the fuel system and fuel samples revealed the presence of super absorbent polymers (SAP), a type of sodium polyacrylate used in airport fuel handling filter monitors to remove water.
Findings
- The primary cause of the engine damage was thermal degradation caused by a localized hot streak within the combustion chamber.
- This thermal event was triggered because fuel atomization and mixing were disturbed, likely due to the impairment of fuel nozzle valves.
- The fuel nozzles were contaminated with super absorbent polymers (SAP) that had bypassed the aircraft's fuel filters and strainers.
- These SAP particles, which can swell into a gel upon contact with water, entered the fuel nozzles and hampered the movement of their internal components.
- The contamination was introduced via the airport's fuel supply system.