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Singapore Airlines Flight 368 Engine Fire
Ng JunshengHead (Technical)/Senior Air Safety Investigation
Transport Safety Investigation Bureau
3rd Annual Singapore Aviation Safety Seminar29 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
• 1st 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
Previously Now
MFOHE SB implementation
- By next engine shop visit - By August 2017
Operationalprocedures for in-flight fuel leak
None - Interim in-flight procedure availablein event of MFOHE fuel leak
- Reduce likelihood of fire after landing
Engine manufacturer diagnostics algorithm
- Developed based on 2014 event- High false alarm rate- No real time detection
- 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?