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?