boeing 777 g-ymmm london heathrow 17 jan ’08
DESCRIPTION
Boeing 777 G-YMMM London Heathrow 17 Jan ’08. BRIEFING TO IASCC 9 September 2010. LHR - BEI – LHR Fuel 79,000 kg ( No 3 Jet Fuel, PRC ) 3 flt - 13 cabin - 136 pax Uneventful flight ( Min temps: SAT -76 ºC; TAT -45 ºC; Fuel - 34 ºC ) TOD predicted fuel 10,000 kg. 1,600 ft agl to TD - PowerPoint PPT PresentationTRANSCRIPT
Slide 1Air AccidentsInvestigationBranch
Boeing 777 G-YMMMBoeing 777 G-YMMM
London HeathrowLondon Heathrow
17 Jan ’0817 Jan ’08
BRIEFING TO IASCC 9 September 2010BRIEFING TO IASCC 9 September 2010
Slide 2Air AccidentsInvestigationBranch
LHR - BEI – LHRFuel 79,000 kg (No 3 Jet Fuel, PRC)
3 flt - 13 cabin - 136 pax
Uneventful flight ( Min temps: SAT -76ºC; TAT -45ºC; Fuel -34ºC )
TOD predicted fuel 10,000 kg
Slide 3Air AccidentsInvestigationBranch
Thrust Levers
EPR actual and commandFMV (QAR)
Fuel Flow
1,600 ft agl to TD4 sec grid spacing
Slide 4Air AccidentsInvestigationBranch
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
Slide 5Air AccidentsInvestigationBranch
Accident Site
Slide 6Air AccidentsInvestigationBranch
Aircraft examination
• No pre-existing defects found with electrical, hydraulic, autoflight, navigation systems or flying controls
• HIRF/EMI eliminated by testing – the power levels required to affect the EEC would have affected the electrical, navigation and communications system first.
Slide 7Air AccidentsInvestigationBranch
Fuel system description
Slide 8Air AccidentsInvestigationBranch
Reconstruction of Left Wing Fuel System
Engine
Centre tank
Main tank
Strut pipes
Slide 9Air AccidentsInvestigationBranch
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
Slide 10Air AccidentsInvestigationBranch
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.
Slide 11Air AccidentsInvestigationBranch
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 their surroundings.
• -18 Deg C– Crystals adhere to each other and
become larger.• Below -20 Deg C little is known about
the properties of the ice.
Slide 12Air AccidentsInvestigationBranch
Fuel testing
• Fuel was of good quality.• Fuel freezing point was -57 Deg C.• Compared with 1,245 batches of Jet
A-1 tested in UK during 2007.– Distillation range average.– Freezing point slightly below average.
Slide 13Air AccidentsInvestigationBranch
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 spread
across 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.
Slide 14Air AccidentsInvestigationBranch
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.
Slide 15Air AccidentsInvestigationBranch
Beaker Tests
Slide 16Air AccidentsInvestigationBranch
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
Slide 17Air AccidentsInvestigationBranch
Spar Valve
Boost Pump
FOHE
Sight Glass
Inlet Screen
Flexible Hose
Sight Glass
LP/HP Pump
Boeing Proprietary
Layout of fuel Components on the Boeing Fuel Rig
Slide 18Air AccidentsInvestigationBranch
FOHE fitted to fuel rig
Slide 19Air AccidentsInvestigationBranch
Ice collecting on pump inlet screen
Slide 20Air AccidentsInvestigationBranch
Icing of FOHE
Slide 21Air AccidentsInvestigationBranch
Aircraft fuel pipes
Strut pipes
LP pump
Fuel pipes in main tank
Slide 22Air AccidentsInvestigationBranch
Fuels Lab Test #156Tube Inspections (Cont.)
Slide 23Air AccidentsInvestigationBranch
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 the FOHE 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.
Slide 24Air AccidentsInvestigationBranch
Data Mining"the extraction of previously
unknown, and potentially useful information from significant
quantities of data“
Slide 25Air AccidentsInvestigationBranch
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 -22 degC
Slide 26Air AccidentsInvestigationBranch
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
Slide 27Air AccidentsInvestigationBranch
The accident flight WAS NOT unique with respect to fuel temperatures
experienced during takeoff, cruise or approach phases
Slide 28Air AccidentsInvestigationBranch
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
Slide 29Air AccidentsInvestigationBranch
1.Fuel Temperature at take off below 0°C and remaining below 0°C during all phases of flight
2.Max Fuel Flow in cruise less than 10,000 pph3.Fuel Temperature during approach less than -15°C 4.Max Fuel Flow greater than 10,000 pph during
approach5.Max Fuel Flow during descent less than 10,000 pph
ONLY MMM ACCIDENT FLIGHT MET ALL 5 CRITERIA FROM ~13,000 FLIGHTS.
Slide 30Air AccidentsInvestigationBranch
Investigation Summary
• Engines rolled back due to reduced fuel flow with no increase although FMV opens fully.
• No technical problem with the aircraft or its systems that could explain the event
• Only physical evidence – HP pump cavitation
• Reasons for HP pump cavitation – a restriction of the fuel flow to the pump
Slide 31Air AccidentsInvestigationBranch
Testing showed:
• Ice can accrete on:– Fuel tank surfaces– Boost pump Inlet screen– Pipework – both rigid and flexible– Valves within the fuel system
Slide 32Air AccidentsInvestigationBranch
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 certain temperatures and below certain fuel flows, the FOHE can successfully melt the ice)
• The system needs to be ~95% blocked to cause the reduced fuel flow
• Ice can accrue within the airframe fuel system and be released, dependent on fuel temperatures and flow rates
Slide 33Air AccidentsInvestigationBranch
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
flows whilst the fuel temperature was in the ‘sticky’ range
• The ice was suddenly released, probably due to demands for higher fuel flow during final approach, but could be due to other factors such as increasing temperatures or turbulence
• The sudden ‘avalanche’ of ice blocked the FOHE, which was unable to melt it
• G-YMMM was always within its certificated operating envelope and there was no evidence of abnormal water quantities in the fuel
• No tests for this threat existed at the time of certification (and will they in the future?)
Slide 34Air AccidentsInvestigationBranch
AAIB Safety Recommendations.These included:
• Interim flight crew procedures to clear accumulated ice at a safe altitude
• Modifying the FOHE to resist this unforeseen threat (already underway by Rolls-Royce)
• Investigating other airframe/engine combinations for vulnerability to this phenomenon
• Changing certification requirements to accommodate the new threat
Slide 35Air AccidentsInvestigationBranch
Safety Recommendation 2009-032 – Issued 12 March 2009
It is recommended that the Federal Aviation Administration and the European Aviation Safety Agency jointly conduct research into ice accumulation and subsequent release mechanisms within aircraft and engine fuel systems.
Slide 36Air AccidentsInvestigationBranch
Questions?