Engine Fire Ng Junsheng Head (Technical)/Senior Air Safety - - PowerPoint PPT Presentation

Singapore Airlines Flight 368 Engine Fire

Ng Junsheng

Head (Technical)/Senior Air Safety Investigation Transport Safety Investigation Bureau

3rd 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:
• TSIB Singapore
• NTSB
• Advisors from engine, aircraft manufacturer & FAA
• Field investigation in Singapore
• Engine and component teardown in US

Investigation Process

• Scope of investigation included:
• Identifying ignition sequence and fire development
• Reviewing regulatory and design issues
• 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:
• Right engine oil system
• Various areas within right engine
• Fan air flow path
• High velocity of airflow around engine in-flight
• Unsuitable for ignition and sustained combustion
• On landing, thrust reversers deployed
• Airflow over core exhaust nozzle reduced
• Most significant reduction – area aft of turkey feather

seal

• Hot surface ignition occurred
• 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:
• 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

• 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
• 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
• Similarity in design
• 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:
• Diffusion bonding – adhesion of tubes to baffle walls
• 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

• Corrective actions required by next engine shop visit
• Event MFOHE not incorporated with SB
• 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
• n return journey
• TOTALIZER fuel quantity less than CALCULATED fuel

quantity

• Should have proceeded on to FUEL LEAK checklist
• Crew believed CALCULATED fuel quantity was not valid

due to:

• Input changes to flight management system
• No longer on planned flight route
• 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:
• FUEL LEAK checklist cannot be performed at unequal

thrust setting

• 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

• In line with operator’s training
• 1st communication, FC informed flight crew
• 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
• FC confirmed fire under control
• Maintained initial recommendation for disembarkation
• Swifter decision on evacuation desired
• Possible resources to aid decision making not utilised:
• Cabin crew
• Taxiing camera system
• Cockpit escape window

Areas of Safety Concern

Decision making and response during non-normal situation

• Research has shown:
• Decision making under stress may become less

systematic and more hurried

• 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:

• Accelerate MFOHE SB implementation
• 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

Operational procedures for in-flight fuel leak None

• Interim in-flight procedure available

in 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
• Monitor analysis and design issues affecting MFOHE
• Implement improvements where necessary

Safety Recommendations

• 13 further safety recommendations made
• Areas of concern includes:
• Study to understand if cracks may develop in crimped

tubes that have no history of cracking

• Evaluate need to periodically inspect MFOHE internal

components

• Evaluate need for guidance to perform leak check with

engines operated at unequal thrust

• Improve sensitivity of fuel leak detection during

maintenance checks

Safety Recommendations

• Areas of concern includes (continued):
• Review airworthiness control system ensure expeditious

implementation of corrective actions

• Ensure emergency and non-normal checklists are

performed correctly

• 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?