British Airways Boeing 777 G-YMMM LHR accident

5/21/2018 British Airways Boeing 777 G-YMMM LHR accident

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Slide 1Air AccidentsInvestigation

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Boeing 777 G-YMMM

London Heathrow

17 Jan 8

BRIEFING TO IASCC 9 September 2010


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LHR - BEI

LHR

Fuel 79,000 kg

(No 3 Jet Fuel, PRC)

3 flt - 13 cabin - 136 pax

Uneventful flight

( Min temps: SAT -76C; TAT -45C; Fuel -34C )

TOD predicted fuel 10,000 kg


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Thrust

Levers

EPR actual

and command

FMV (QAR)

Fuel Flow

1,600 ft agl

to TD

4 sec grid

spacing


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PALT

Min Fuel Temp in

cruise -34 deg C TAT

Accident Flight Track from FDR

Takeoff fuel temp

was -2 deg C

Fuel temp at

590 ft agl was

-22 deg C

FDR Data


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Accident Site


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Aircraft examination

No pre-existing defects found with

electrical, hydraulic, autoflight, navigation

systems or flying controls

HIRF/EMI eliminated by testingthe

power levels required to affect the EEC

would have affected the electrical,

navigation and communications systemfirst.


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Fuel system description


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Reconstruction of Left Wing Fuel

System

Engine

Centre tank

Main tank

Strut pipes


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Engine - HP pump cavitation marks

Fuel Pump 0019 (LH Engine)

Built Oct 99, Never overhauled A/C Boost pump debris on Impellor

Abnormal cavitation markings on bearing

thrust faces and HP housing at discharge

window


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Types of water in fuel

Dissolved water

Molecule of water attached to a hydrocarbon

molecule. As temperature drops becomes entrained

water. Undissolved water

Entrained water, often referred to as suspended.

Suspended as tiny droplets in the fuel settles to form free

water. Free water

Visible water that collects on bottom of tanks.


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Water ice in fuel Only entrained and free water form ice.

Ice crystals form at -1 to -3 Deg C.

Density similar to fuel, so float in fuel.

Critical Icing Temperature ~ -8 Deg C.

When ice crystals start to stick to theirsurroundings.

-18 Deg C

Crystals adhere to each other and becomelarger.

Below -20 Deg C little is known about theproperties of the ice.


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Fuel testing

Fuel was of good quality.

Fuel freezing point was -57 Deg C.

Compared with 1,245 batches of Jet A-1tested in UK during 2007.

Distillation range average.

Freezing point slightly below average.


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Slide 13Air Accidents

InvestigationBranch

Estimated water content in fuel

during accident flight

Dissolved water, 3 ltr (40ppm).

Undissolved water (entrained and free),

maximum of 2 ltr (30 ppm).

This Water would have been evenly spreadacross the fuel system at the start of the flight.

Water also introduced through the vent system

during the flight, approximately 0.14 ltr. Plus any water remaining from previous flights.


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Testing by Boeing

Beaker Test Small scale test in climatic chamber.

Used simulated fuel system components.

Establish how ice might accumulate and restrict flow.

Fuel rig testing

Actual components from B777.

Establish if ice could build up in the system and

restrict the flow. Use fuel preconditioned with water or inject water

directly into boost pump inlet.


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Beaker Tests


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Significant temperatures

Water ice forms (-1 to -3C, 31 to 27F)

Sticky range (-8 to -20C, 23 to -4F)

Ice starts to adhere to metal (-9C, 16F)

Ice at most stickiness (-12C, 10F)

Ice adheres strongly to metal surfaces (-17C, 0F)

Ice takes on a more crystalline appearance below -20C, (-4F)

Ice lacks the properties to bridge orifices (-25C, -23F)

Spontaneous formation of ice crystals from super cooled water

(-24C, -11F)

Lowest temperature super cooled water can exist in aviation fuel

(-51C, -60F)

0C

-50C


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InvestigationBranch

Spar Valve

Boost Pump

FOHE

Sight Glass

Inlet Screen

Flexible Hose

SightGlass

LP/HP Pump

Boeing Propr ietary

Layout of fuel Components on the

Boeing Fuel Rig


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InvestigationBranch

FOHE fitted to fuel rig


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Slide 19

Air Accidents

InvestigationBranch

Ice collecting on pump inlet screen


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Slide 20

Air Accidents

InvestigationBranch

Icing of FOHE


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Slide 21

Air Accidents

InvestigationBranch

Aircraft fuel pipes

Strut pipes

LP pump

Fuel pipes in

main tank


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Slide 22

Air Accidents

InvestigationBranch

Fuels Lab Test #156

Tube Inspections (Cont.)


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Slide 23

Air Accidents

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Findings of rig test

Ice can accrete on the inside of fuel pipes and

on inlet screens.

Thickness depend on fuel temp and flow.

It is possible to restrict the flow through theFOHE with cold fuel and low levels of water

simulating a sudden release of ice.

Blocks of ice unlikely to have caused restriction.

Problems with repeatability of some of the

results.


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Slide 24

Air Accidents

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Data Mining

the extraction of previously unknown, and

potentially useful information from significant

quantities of data


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Slide 25

Air Accidents

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Facts from the accident flight

Fuel temperature at takeoff -2 degC

Minimum fuel temperature in the cruise -34 degC

Minimum TAT in the cruise -45 degC

Fuel temperature on final approach -22degC


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Slide 26

Air Accidents

InvestigationBranch

-60.00

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

10.00

-45 -40 -35 -30 -25 -20 -15 -10 -5 0

TAT

Fuel Temp

Fuel Temp vs TAT

TAT1

BA/United/Cathay ~60,000 flights

(Apr06 to Mar 08)

Minimum fuel temperature, -12 deg C and below

G-YMMM

-34 Fuel

-45 TAT

Fuel Temp

TAT


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Slide 27

Air Accidents

InvestigationBranch

The accident flight WAS NOTunique with

respect to fuel temperatures experienced

during takeoff, cruise or approach phases


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Slide 28

Air Accidents

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Through the complementary use of data mining and

laboratory tests, efforts were focused on the

activity of two parameters:

Fuel Flow and Fuel Temperature

The following slide identifies the combination of Fuel

Flow and Fuel Temperature parameters which

were unique to the accident flight


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Slide 29

Air Accidents

InvestigationBranch

1.Fuel Temperature at take off below 0C and

remaining below 0C during all phases of flight2.Max Fuel Flow in cruise less than 10,000 pph

3.Fuel Temperature during approach less than -15C

4.Max Fuel Flow greater than 10,000 pph duringapproach

5.Max Fuel Flow during descent less than 10,000 pph

ONLY MMM ACCIDENT FLIGHT MET ALL 5

CRITERIA FROM ~13,000 FLIGHTS.


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Slide 30

Air Accidents

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Investigation Summary

Engines rolled back due to reduced fuelflow with no increase although FMV opensfully.

No technical problem with the aircraft or itssystems that could explain the event

Only physical evidenceHP pump

cavitation Reasons for HP pump cavitationarestriction of the fuel flow to the pump


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Slide 31

Air Accidents

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Testing showed:

Ice can accrete on:

Fuel tank surfaces

Boost pump Inlet screen

Pipeworkboth rigid and flexible

Valves within the fuel system


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Slide 32

Air Accidents

InvestigationBranch

Testing also showed

The FOHE can become blocked when water is

introduced to cold fuel creating a snowball The effect of the blockage changes at different

fuel temperatures & fuel flows (above certaintemperatures and below certain fuel flows, the

FOHE can successfully melt the ice) The system needs to be ~95% blocked to causethe reduced fuel flow

Ice can accrue within the airframe fuel systemand be released, dependent on fueltemperatures and flow rates


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Slide 33

Air Accidents

InvestigationBranch

Summary Fuel flow restricted due to ice formed from water that was

naturally occurring in the fuel

The ice accreted over a long period, with low fuel flowswhilst the fuel temperature was in the sticky range

The ice was suddenly released, probably due to demandsfor higher fuel flow during final approach, but could be dueto other factors such as increasing temperatures orturbulence

The sudden avalanche of ice blocked the FOHE, whichwas unable to melt it

G-YMMM was always within its certificated operatingenvelope and there was no evidence of abnormal waterquantities in the fuel

No tests for this threat existed at the time of certification(and will they in the future?)

AAIB S f t R d ti


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Slide 34

Air Accidents

InvestigationBranch

AAIB Safety Recommendations.

These included:

Interim flight crew procedures to clearaccumulated ice at a safe altitude

Modifying the FOHE to resist this

unforeseen threat (already underway byRolls-Royce)

Investigating other airframe/enginecombinations for vulnerability to this

phenomenon Changing certification requirements to

accommodate the new threat


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Slide 35

Air Accidents

InvestigationBranch

Safety Recommendation 2009-032

Issued 12 March 2009

t is recommended that the Federal Aviation Administration

and the European Aviation Safety Agency jointly conductresearch into ice accumulation and subsequent release

echanisms within aircraft and engine fuel systems.


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Slide 36

Air Accidents

Investigation

Questions?

British Airways Boeing 777 G-YMMM LHR accident

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