Post on 11-Oct-2015
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5/21/2018 British Airways Boeing 777 G-YMMM LHR accident
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Slide 1Air AccidentsInvestigation
Branch
Boeing 777 G-YMMM
London Heathrow
17 Jan 8
BRIEFING TO IASCC 9 September 2010
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Slide 2Air AccidentsInvestigation
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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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Slide 3Air AccidentsInvestigation
Branch
Thrust
Levers
EPR actual
and command
FMV (QAR)
Fuel Flow
1,600 ft agl
to TD
4 sec grid
spacing
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Slide 4Air AccidentsInvestigation
Branch
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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Slide 5Air AccidentsInvestigation
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Accident Site
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Slide 6Air AccidentsInvestigation
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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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Slide 7Air AccidentsInvestigation
Branch
Fuel system description
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Slide 8Air AccidentsInvestigation
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Reconstruction of Left Wing Fuel
System
Engine
Centre tank
Main tank
Strut pipes
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Slide 9Air AccidentsInvestigation
Branch
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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Slide 10Air AccidentsInvestigation
Branch
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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Slide 11Air AccidentsInvestigation
Branch
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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Slide 12Air AccidentsInvestigation
Branch
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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Slide 14Air Accidents
InvestigationBranch
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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Slide 15Air Accidents
InvestigationBranch
Beaker Tests
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Slide 16Air Accidents
InvestigationBranch
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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Slide 17Air Accidents
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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Slide 18Air Accidents
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
InvestigationBranch
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
InvestigationBranch
Data Mining
the extraction of previously unknown, and
potentially useful information from significant
quantities of data
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Slide 25
Air Accidents
InvestigationBranch
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
InvestigationBranch
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
InvestigationBranch
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
InvestigationBranch
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?