Singapore Airlines Flight 368 Engine Fire Ng Junsheng Head (Technical)/Senior Air Safety Investigation Transport Safety Investigation Bureau 3 rd Annual Singapore Aviation Safety Seminar 29 March 2017
What Happened? 27 June 2016, Boeing 777-300ER departed Singapore 2 hrs into flight, low oil quantity indication for right engine Subsequently, vibration felt in control column and cockpit floor Decision to return on Singapore with right engine at idle power After landing, fire observed in vicinity of right engine Fire extinguished, disembarkation via mobile stairs
Scope Investigation Process Key Findings Areas of Safety Concern Safety Improvements Safety Recommendations
Investigation Process Investigation conducted in accordance with ICAO Annex 13 Aim to improve safety, not to apportion blame or liability Investigation team included: o TSIB Singapore o NTSB o Advisors from engine, aircraft manufacturer & FAA Field investigation in Singapore Engine and component teardown in US
Investigation Process Scope of investigation included: o Identifying ignition sequence and fire development o Reviewing regulatory and design issues o Human factors in relation to flight operation and decision making
Key Findings Fuel found in areas usually filled with oil A cracked tube found within the Main Fuel Oil Heat Exchanger (MFOHE) of right engine
Key Findings Fuel leak into: o Right engine oil system o Various areas within right engine o Fan air flow path High velocity of airflow around engine in-flight o Unsuitable for ignition and sustained combustion On landing, thrust reversers deployed o Airflow over core exhaust nozzle reduced o Most significant reduction area aft of turkey feather seal o Hot surface ignition occurred o Accumulated fuel in fan duct distributed over lower surface of wing
Key Findings Turkey feather seal Area discoloured due to high temperature exposure
Key Findings Fire development: o Into engine core: 1. Fire progressed forward in fan duct 2. Through reverser blocker doors 3. Into booster 4. Progressed to high pressure compressor & variable bleed valve system o Fire on runway - Engine was shut down - During spool down, excess fuel in booster cavity discharged through fan duct - Collected on runway and caught fire o Fuel distributed over lower surface of right wing caught fire
Areas of Safety Concern Design of MFOHE Event MFOHE design revised based on original MFOHE designed for basic GE90 engine Met all regulatory requirements through combination of o Similarity in design o Actual testing No tube cracking in original MFOHE design Tube cracking only in high service hour MFOHE units based on revised design
Areas of Safety Concern Design of MFOHE Root cause of cracked tubes: o Diffusion bonding adhesion of tubes to baffle walls o Stress concentration in crimped areas contributing factor Potential for all tubes to crack, regardless if crimped MFOHE designed for unlimited service lifespan No periodic inspection requirement on MFOHE internal portion
Areas of Safety Concern Resolution for cracked tube problem Service Bulletin (SB) in place after event of lesser consequence in Aug 14 o Corrective actions required by next engine shop visit Event MFOHE not incorporated with SB o Last shop maintenance before SB issuance Urgency for SB compliance based on FAA s Continuous Airworthiness Assessment Methodologies (CAAM) Despite adherence to CAAM, cracked tube recurred with a more severe consequence
Areas of Safety Concern Execution of checklist Flight crew encountered FUEL DISAGREE message on return journey TOTALIZER fuel quantity less than CALCULATED fuel quantity o Should have proceeded on to FUEL LEAK checklist Crew believed CALCULATED fuel quantity was not valid due to: o Input changes to flight management system o No longer on planned flight route o At last routine fuel check, 600 kg more fuel than expected
Areas of Safety Concern Execution of checklist Crew performed own calculation which tallied well with TOTALIZER value Crew concluded FUEL DISAGREE was spurious FUEL DISAGREE checklist was not performed as intended Additional observations: o FUEL LEAK checklist cannot be performed at unequal thrust setting o Infrequently used checklist may not be reviewed/ refreshed after initial training
Areas of Safety Concern Decision making and response during non-normal situation No cockpit indication of fire Flight crew informed of fire by ATC Flight crew depended on fire commander (FC) as primary information source o In line with operator s training 1 st communication, FC informed flight crew o trying to contain fire, described fire as pretty big FC assessed no risk of fire spreading, recommended disembarkation
Areas of Safety Concern Decision making and response during non-normal situation Pilot-in-command aware decision to evacuate lay with him After over 2 minutes o FC confirmed fire under control o Maintained initial recommendation for disembarkation Swifter decision on evacuation desired Possible resources to aid decision making not utilised: o Cabin crew o Taxiing camera system o Cockpit escape window
Areas of Safety Concern Decision making and response during non-normal situation Research has shown: o Decision making under stress may become less systematic and more hurried o Fewer alternative choices are considered Not possible for checklists to include all possible emergency/abnormal situation Critical to have ability to consider alternatives/ available resources not dealt with by any checklist
Safety Improvements 25 Jul 16, TSIB (then AAIB Singapore) made safety recommendations to: o Accelerate MFOHE SB implementation o Review need for interim operational procedures should flight crew encounter similar fuel leak in-flight MFOHE SB implementation Operational procedures for in-flight fuel leak Engine manufacturer diagnostics algorithm Previously Now - By next engine shop visit - By August 2017 None - Developed based on 2014 event - High false alarm rate - No real time detection - Interim in-flight procedure available in event of MFOHE fuel leak - Reduce likelihood of fire after landing - Improved detection capability - Reduced false alarm rate - Real time monitoring by integration into B777 ACMF
Safety Improvements No instance of leak in MFOHEs incorporated with SB FAA working with engine manufacturer o Monitor analysis and design issues affecting MFOHE o Implement improvements where necessary
Safety Recommendations 13 further safety recommendations made Areas of concern includes: o Study to understand if cracks may develop in crimped tubes that have no history of cracking o Evaluate need to periodically inspect MFOHE internal components o Evaluate need for guidance to perform leak check with engines operated at unequal thrust o Improve sensitivity of fuel leak detection during maintenance checks
Safety Recommendations Areas of concern includes (continued): o Review airworthiness control system ensure expeditious implementation of corrective actions o Ensure emergency and non-normal checklists are performed correctly o Develop flight crews ability to consider alternatives/ resources in situations no dealt with by any checklist
Final report available at: https://www.mot.gov.sg/about-mot/air- Transport/AAIB/Investigation-Report/
Thank You Questions?