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 trying to contain fire, described fire as “pretty big” o • 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 Previously Now MFOHE SB - By next engine shop visit - By August 2017 implementation Operational None - Interim in-flight procedure available procedures for in event of MFOHE fuel leak in-flight fuel - Reduce likelihood of fire after leak landing Engine - Developed based on 2014 event - Improved detection capability manufacturer - High false alarm rate - Reduced false alarm rate diagnostics - No real time detection - Real time monitoring by integration algorithm 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 /
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