Feb 22, 2008
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AAIB Bulletin S1/2008 SPECIAL Farnborough House Berkshire Copse Road Aldershot, Hants GU11 2HH Tel: 01252 510300 Telex: 858119 ACCINV G Fax: 01252 376999 Department for Transport This bulletin contains facts which have been determined up to the time of issue. This information is published to inform the aviation industry and the public of the general circumstances of accidents and must necessarily be regarded as tentative and subject to alteration or correction if additional evidence becomes available. Extracts can be published without specific permission providing that the source is duly acknowledged.
c Crown copyright 2008 ACCIDENT Aircraft Type and Registration: Boeing 777-236 ER, G-YMMM No & Type of Engines: 2 Rolls-Royce RB211 Trent 895-17 turbofan engines Year of Manufacture: 2001 Date & Time (UTC): 17 January 2008 at 1242 hrs Location: Runway 27L, London Heathrow Airport Type of Flight: Commercial Air Transport (Passenger) Persons on Board: Crew - 16 Passengers - 136 Injuries: Crew - 4 (Minor) Passengers - 1 (Serious) 8 (Minor) Nature of Damage: Aircraft damaged beyond economic repair Commander fs Licence: Airline Transport Pilot fs Licence Commander fs Age: 43 years Commander fs Flying Experience: 12,700 hours (of which 8,500 hours were on type) Last 90 days - 85 hours Last 28 days - 52 hours Information Source: Inspectors Investigation All times in this report are UTC AAIB Special
Bulletin: 1/2008 G-YMMM EW/C2008/01/ 01 c Crown copyright 2008
The investigation
The Air Accidents Investigation Branch (AAIB) was informed of the accident
at 1251 hrs on 17 January 2008 and the investigation commenced immediately. The Chief Inspector of Air Accidents has ordered an Inspector fs
Investigation to be conducted into the circumstances of this accident under
the provisions of The Civil Aviation (Investigation of Air Accidents and
Incidents) Regulations 1996. In accordance with established international
arrangements, the National Transportation Safety Board (NTSB) of the USA, representing the State of Design and Manufacture of the aircraft, has appointed an Accredited Representative to participate fully in
the investigation. The NTSB Accredited Representative is supported by a team which includes additional investigators from the NTSB, the Federal Aviation Administration and Boeing; Rolls-Royce, the engine manufacturer, is also participating fully in the investigation. British Airways, the operator, is
cooperating with the investigation and providing expertise as required and
the CAA and the EASA are being kept informed of developments. Because of the interest within the aviation industry, and amongst the travelling public, it
is considered appropriate to disseminate the results of the initial
investigation as soon as possible. This Bulletin is in addition to the
Initial Report, published on 18 January 2008, and a subsequent update
published on 23 January 2008. As the investigation has developed, additional
data has been derived from non-volatile memory within specific systems of
the aircraft. This has allowed previously reported data to be refined. One
Safety Recommendation has been made.
History of the flight
The aircraft was on a scheduled flight from Beijing, China, to London
(Heathrow) and departed Beijing at 0209 hrs; the flight was uneventful until
the later stages of the approach into Heathrow. During the descent, from
Flight level (FL) 400 the aircraft entered the hold at Lamborne at FL110; it
remained in the hold for approximately five minutes, during which time it
descended to FL90. The aircraft was radar vectored for the ILS approach to
Runway 27L at Heathrow and subsequently stabilised on the ILS with the
autopilot and autothrottles engaged. At 1,000 ft the aircraft was fully
configured for the landing, with the landing gear down and flap 30 selected.
The total fuel on board was indicating 10,500 kg, which was distributed
almost equally between the left and right main fuel tanks, with a minor
imbalance of about 300 kg. The fuel crossfeed valves indicated that they
were closed and they had not been operated during the flight. The first
officer took control for the landing at a height of approximately 780 ft, in
accordance with the briefed procedure, and shortly afterwards the
autothrottles commanded an increase in thrust from both engines. The engines
initially responded but, at a height of about 720 ft, the thrust of the
right engine reduced. Some seven seconds later, the thrust reduced on the
left engine to a similar level. The engines did not shut down and both
engines continued to produce thrust at an engine speed above flight idle,
but less than the commanded thrust. The engines failed to respond to further
demands for increased thrust from the autothrottles, and subsequent movement
of the thrust levers fully forward by the flight crew. The airspeed reduced
as the autopilot attempted to maintain the ILS glide slope and by 200 ft the
airspeed had reduced to about 108 kt. The autopilot disconnected at
approximately 175 ft, the aircraft descended rapidly and its landing gear
made contact with the ground some 1,000 ft short of the paved runway surface
just inside the airfield boundary fence. During the impact and short AAIB
Special Bulletin: 1/2008 G-YMMM EW/C2008/01/ 01 c Crown copyright 2008 ground
roll the nose gear collapsed, the right main landing gear separated from the
aircraft and the left main landing gear was pushed up through the wing. The
aircraft came to rest on the paved surface in the undershoot area of Runway
27L. A significant amount of fuel leaked from the aircraft after it came to
rest, but there was no fire. The cabin crew supervised the emergency
evacuation and all occupants left the aircraft via the slides, all of which
operated correctly; eight of the passengers received minor injuries and one
suffered a broken leg. Aircraft information
The aircraft was serviceable on departure from Beijing and there were no
relevant reported defects. It departed with 79,000 kg of Jet A-1 fuel on
board, and the planned arrival fuel at London (Heathrow) was 6,900 kg.
Weather The recorded weather at Beijing, prior to departure, indicated no
significant weather and a surface temperature of -7oC. The aircraft fs
flight plan required it to climb initially to
10,400 m (FL341) before descending back to 9,600 m (FL315) at POLHO (on the
border between China and Mongolia) because of eExtreme Cold f. However, to
accommodate a request from ATC the crew accepted a climb to a cruise
altitude of 10,600 m (FL348), and closely monitored the fuel temperature.
The ambient temperature at FL348 was approximately -65oC and the associated
total air temperature (TAT) was -37oC. Shortly after crossing the Ural
mountains, the aircraft climbed to FL380. There was a region of particularly
cold air, with ambient temperatures as low as -76oC, in the area between the
TAT is measured by a specially designed temperature probe, on the surface of
the aircraft, that brings the air to rest causing an adiabatic increase in
temperature. TAT is higher than static (or ambient) air temperature and is
the value to which the fuel temperature will drift. Urals and Eastern
Scandinavia. The Met Office described the temperature conditions during the
flight as eunusually low compared to the average, but not exceptional f. The
lowest TAT recorded during the flight was .45oC, and the minimum recorded
fuel temperature was -34oC. The fuel temperature in flight must not reduce
to a temperature colder than at least 3oC above the fuel freezing point of
the fuel being used. The specified freezing point for Jet A-1 fuel is -47oC;
analysis of fuel samples taken after the accident showed the fuel onboard
the aircraft had an actual freezing point of -57oC.
On arrival at Heathrow, the surface wind was from 210o at 10 kt, the
visibility was greater than 10 km, the cloud was scattered at 800 ft and
broken at 1,000 ft, the surface temperature was +10oC and the dew point was
+8oC. The flight crew reported that they were visual with the runway at
about 1,000 ft agl. Recorded data
The aircraft was fitted with a Digital Flight Data Recorder (DFDR), a
Cockpit Voice Recorder (CVR) and a Quick Access Recorder (QAR). The CVR and
DFDR were successfully downloaded at the AAIB laboratories at Farnborough
and both records covered the critical final stages of the flight. The QAR
was downloaded with the assistance of British Airways and the equipment
manufacturer. Data from the non-volatile memory of various systems were also
available. The recorded data indicates that there were no anomalies in the
major aircraft systems. The autopilot and the autothrottle systems behaved
correctly and the engine control systems were providing the correct commands
prior to, during, and after, the reduction in thrust. Engineering
examination
The aircraft was recovered from the accident site to a AAIB Special
Bulletin: 1/2008 G-YMMM EW/C2008/01/ 01 c Crown copyright 2008 secure
location for detailed examination. There were no indications of any
pre-existing problems with any of the aircraft systems.
During the impact the right main landing gear separated from the aircraft
rupturing the rear right wall of the centre fuel tank. The two front wheels
of the right main landing gear broke away and struck the rear right fuselage
penetrating the cabin at seat height adjacent to rows 29/30. Additionally,
the right main landing gear damaged the wing-to-body fairing and penetrated
the rear cargo hold, causing damage to, and leakage from, the passenger
oxygen cylinders. The engines, their control systems and the fuel system
were the focus of a detailed examination.
Engines
Examination of the engines indicated no evidence of a mechanical defect or
ingestion of birds or ice. Data, downloaded from the Electronic Engine
Controllers
(EECs) and the QAR, revealed no anomalies with the control system operation.
At the point when the right engine began to lose thrust the data indicated
that the right engine EEC responded correctly to a reduction in fuel flow to
the right engine, followed by a similar response from the left EEC when fuel
flow to the left engine diminished. Data also revealed that the fuel
metering valves on both engines correctly moved to the fully open position
to schedule an increase in fuel flow. Both fuel metering units were tested
and examined, and revealed no pre-existing defects.
Both engine low pressure fuel filters were clean. The fuel oil heat
exchangers (FOHE) in both engines were free of blockage. The right FOHE was
clear of any debris, however the left engine FOHE had some small items of
debris on its fuel inlet bulkhead. The high pressure filters were clean. The
variable stator vane controllers and the fuel burners were examined and
found to be satisfactory. Detailed examination of both the left and right
engine high pressure fuel pumps revealed signs of abnormal cavitation on the
pressure-side bearings and the outlet ports. This could be indicative of
either a restriction in the fuel supply to the pumps or excessive aeration
of the fuel. The manufacturer assessed both pumps as still being capable of
delivering full fuel flow.
Fuel system
Several fuel samples were taken from the fuel tanks, pipe lines and filter
housings prior to the examination of the fuel system and these are currently
being examined at specialist laboratories. Initial results confirm that the
fuel conforms to Jet A-1 specifications and that there were no signs of
contamination or unusual levels of water content. A sump sample taken from
the left and right main fuel tanks shortly after the accident revealed no
significant quantities of water. Samples from the centre tank had been
contaminated by fire fighting foam and hydraulic fluid: this contamination
was a consequence of the rupture of the right rear wall of the centre tank.
A detailed examination of the fuel tanks revealed no pre.existing defects
except for a loose union in the left main tank at its inner wall; the union
formed part of the centre tank to left main tank fuel scavenge line. Some
small items of debris were discovered in the following locations:
1. Right main tank . a red plastic sealant scraper approximately 10 cm x 3
cm under the suction inlet screen. AAIB Special Bulletin: 1/2008 G-YMMM
EW/C2008/01/ 01 c Crown copyright 2008
2. Left main tank, water scavenge inlet - a piece of black plastic tape,
approximately 5 cm square; a piece of brown paper of the same size and
shape, and a piece of yellow plastic.
3. Right centre tank override pump . a small piece of fabric or paper found
in the guillotine valve of the pump housing.
4. Left centre tank water scavenge jet pump . small circular disc, 6 mm in
diameter, in the motive flow chamber. The relevance of this debris is still
being considered. Examination of the fuel surge tanks showed no signs of
blockage of the vent scoops and flame arrestors. Neither pressure relief
valve had operated; the relief valves were tested and found to be operate
normally. The fuel boost pumps, and their associated low pressure switches,
were tested and examined and found to be satisfactory. A pressure and
suction test of the engine fuel feed manifold, from the fuel boost pumps to
the engine, did not reveal any significant defects. Similarly, a visual
examination of the fuel feed lines, using a boroscope, did not reveal any
defects or restrictions. A test of the fuel quantity processor unit (FQPU)
was satisfactory and its non-volatile memory did not reveal any defects
stored prior to the accident. A test of the fuel temperature probe, located
in the left main fuel tank, was satisfactory.
Maintenance
The aircraft fs fuel tanks were last checked for water in the fuel on the 15
January 2008 at Heathrow; this was prior to its refuelling for the outboard
sector to Beijing. Footnote A check for water in the fuel tank is carried
out by draining fluid from the sump drains located at the lowest point of
each fuel tank in its eon-ground f attitude. Access by maintenance
personnel, to the aircraft fs fuel tanks, had last taken place during
maintenance activity in 2005. The last scheduled maintenance activity on the
aircraft was on the 13 December 2007.
Spar valves
On examination, both of the engine spar valves were found to be OPEN,
allowing the fuel leak evident at the accident site.
The spar valves are designed to shut off the fuel supply to the engines
following the operation of the fuel control switches or after operation of
the fire handles in the cockpit. Their function is to cut off the fuel flow
to the engine in the event of an engine fire or an accident. Each valve has
two separate electrical wire paths which can be used to supply power to shut
the valve; the first is via a run/cut-off relay, controlled by the fuel
control switches, the other is directly from the fire handles. The wiring on
G-YMMM was as originally designed and manufactured, and such that when the
fire handle was operated, it isolated the power supply to the run/cutoff
relay. When tested, the run/cut-off relays for the left and right engines
were still in the valve OPEN position, despite the fuel control switches
being set to cut-off. The fire handles had also been pulled and the engine
fire bottles had been fired. Therefore the fire handles had been operated
prior to the fuel control switches. The left spar valve circuit breaker (CB)
had been tripped. This was due to damaged wiring to the valve as a result of
the left main landing gear being forced upward through the conduit at the
initial impact. The tripping of the CB meant there was no means of
electrically closing the left spar valve. Similar damage was also evident to
the right spar valve wiring, however, in this instance the CB had remained
set.
AAIB Special Bulletin: 1/2008 G-YMMM EW/C2008/01/ 01 c Crown copyright 2008
Published February 2008 Examination and tests of the wiring identified that,
in the case of the right engine, the valve CLOSE wire from the run/ cut-off
relay was still continuous. This could have allowed the valve to operate had
the fuel switch been operated before the fire handle
Boeing had issued a Service Bulletin (SB 777-28-0025) which advised the
splicing together of the wires for the fuel control switches and the fire
handles to avoid the need to sequence their operation. An FAA airworthiness
directive requires this SB to be completed by July 2010. This had not yet
been incorporated on G-YMMM; however, had it been incorporated, the right
spar valve should have closed when the fuel control switch was operated.
The evacuation checklist for the Boeing 777, issued by Boeing, shows
operation of the fuel control switches to cut-off prior to operation of the
fire handles. This sequence allows for both CLOSE paths to the spar valve to
be exploited and increases the likelihood that the spar valves close before
electrical power to the spar valves is isolated. However, if the fire handle
is operated first, then only a single path is available.
The operator fs evacuation checklist, for which Boeing had raised no
technical objection, required the commander to operate the fuel control
switches whilst the first officer operated the fire handles, this was in
order to reduce the time required to action the checklist. These actions
were carried out independently, with no measure in place to ensure the
correct sequencing. The evacuation drill was placarded on the face of the
control column boss, directly in front of each pilot. An evacuation
checklist with the division of independent tasks between the crew leaves a
possibility that the fire handles could be operated before the fuel control
switches which, with fire handle to spar valve wire damage, could leave the
engine fuel spar shut-off valves in an OPEN position. This occurred in this
accident, and resulted in the loss of fuel from the aircraft. This was not
causal to the accident but could have had serious consequences in the event
of a fire during the evacuation. It is therefore recommended that:
Safety Recommendation 2008-009 Boeing should notify all Boeing 777 operators
of the necessity to operate the fuel control switch to cut-off prior to
operation of the fire handle, for both the fire drill and the evacuation
drill, and ensure that all versions of its checklists, including electronic
and placarded versions of the drill, are consistent with this procedure.
Boeing has accepted this recommendation. On 15 February 2008 Boeing issued a
Multi Operator Message, which advised operators to ensure that gevacuation
and engine fire checklists specifiy that the fuel control switches are
placed in the cut-off position prior to the operation of the fire handles h.
This advice only relates to those aircraft that have not had Boeing SB
777-28-0025 incorporated. Boeing also recommends that operators review their
engine fire and evacuation checklists (Quick Reference Handbook, Electronic
and Placard) to make sure that they are consistent with this advice.
Continuing investigation
Investigations are now underway in an attempt to replicate the damage seen
to the engine high pressure fuel pumps, and to match this to the data
recorded on the accident flight. In addition, comprehensive examination and
analysis is to be conducted on the entire aircraft and engine fuel system;
including the modelling of fuel flows taking account of the environmental
and aerodynamic effects. |
Air in fuel linked to Heathrow plane crash
By David Millward, Transport Editor
Last Updated: 12:53pm GMT Feb 19, 2008
Air bubbles in fuel could have caused the British Airways Boeing 777
crash-landing at Heathrow, investigators said on Monday night.
The Air Accidents Investigation Branch has focused its attention on
the plane's high-pressure fuel pumps, after a study found they were
damaged and there was debris in the fuel tanks.
Plain Text Attachment [ Scan and Save to Computer ]
The AAIB found no evidence of a mechanical failure
If air got into the fuel it would have prevented the pumps working
properly. This could have led to inadequate fuel reaching the
engines, which then failed to provide the thrust needed to land.
The plane, with 16 crew and 136 passengers on board, landed short of
the runway. Other causes, including frozen or contaminated fuel, bird
strike or computer failure, were ruled out.
Investigators now plan to recreate the damage and compare the black
box recorders' account of last month's flight from Beijing.
Their report said: "Detailed examination of… fuel pumps revealed
signs of abnormal cavitation (air bubbles) on the pressure-side
bearings and the outlet ports. This could be indicative of either a
restriction in the fuel supply to the pumps or excessive aeration of
the fuel."
Investigators found no evidence of mechanical defects or any
anomalies after examining the black box flight recorders.
However they did raise concern about the failure of valves to cut off
fuel supply after the plane landed, which led to fuel leaking from
the aircraft.
"This was not causal to the accident but could have had serious
consequences in the event of a fire during the evacuation," the
report noted.
The valves are designed to stop fuel supply immediately in the event
of an accident or an engine fire.
They should be cut off first - either automatically or manually -
before the fire handle, which works the onboard fire extinguisher, is
turned.
But the original design of the wiring was found to prevent this
happening, leading Boeing to advise airlines to modify this.
The Federal Aviation Authority in Washington has set a deadline of
July 2010 for this work to be done for all 667 Boeing 777s in service.
However this modification had not been carried out on this particular
BA plane.
As a result the two procedures were carried out manually by Peter
Burkill, the captain, and John Coward, his first officer.
With time short, they did so simultaneously. This, however, led to
one of the valves not being cut off, leading to a loss of fuel from
the aircraft.
"It's a bit like turning a fire extinguisher onto an engine before
you have turned off the ignition," one industry expert explained.
But, BA said on Monday night, the two men followed BA's standard
procedures which had been agreed with Boeing.
However the AAIB has told Boeing to instruct airlines to make sure
that the fuel valve is cut off before the fire handle is operated.
"We have already implemented these changes to reflect the latest
advice," a BA spokesman said.
Publishers wishing to reproduce photographs on this page should phone
44 (0) 207 931 2921 or email syndication@telegraph.co.uk
Feb 15, 2008
This snipet of early findings came from several sources such as Boeing-777 power plant engineers, Boeing-777 pilots and feed back from our British cousins.
The magic word is again China. The subject dead Boeing-777 is showing early signs of fuel contamination as to primarily fuel/water ingestion. The flight originated in China. The suspected water mix probably migrated to the bottom of the tank. It was an extremely long flight so cruise occurred with a high fuel/water ratio for most of the flight. During the landing approach phase, as the fuel supply reduced to normal approach quantity, the ratio changed more toward water. Due to the many hours of cruise -50C temp the water in the bottom of the tank was either frozen or of a high viscosity sludge. As power was reduced at some late stage on final approach, the engine fuel pumps provide less suction pump power and as the throttles were advanced --- the fuel filters were now probably clogged. There is also evidence that the RAT had deployed automatically by sensing lack of hydraulic pressure indicating that both engines had now failed. The RAT probably saved the day in that the worlds largest glider still had enough hydraulics to provide flight controls allowing control to the clear way at the end of the runway. The Boeing-777 then slid through the over run and onto the runway that provided a surface that was at least survivable. All aboard survived. Obviously the fuel and the fueling operation originated in China which has repeatedly demonstrated a lack of quality control or concern in many areas.
None of this has yet been officially confirmed. Typically engines do not share much in the way of common components except fuel and in the new age possibly computer software, which is also a player. Based on the complete isolation of the engines the Feds have long ago signed off on the concept that all engines would not fail simultaneously. Now we know differently at this point of the accident investigation Phase One. The NTSB, FAA and the British National Safety Bureau will eventually determine the dual-engine failure as to the primary and secondary causes and factors.
The copilot (First Officer) made the the approach and "landing" which addresses the left seat's (Captain's) cool measure of confidence in the lad.
Note: RAT: Ram air turbine that senses lack of hydraulic pressure and automatically or manually deploys into the airstream.
U.K. Zeros In On Fuel System In 777 Crash
Jan 30, 2008
Thanks to Tom Sheppard for this info. Dick
Had the pleasure of chatting with a member of the NTSB board last night at dinner. Here is what he shared. Aircraft was at 600 ft agl when the right engine started to roll back to slightly above flight idle. The First Officer was flying and auto throttles were engaged. The auto throttles moved the throttles up to catch the decel in airspeed. The right engine did not respond to the movement of the auto throttles. The First Officer disengaged the auto throttles and manually moved both throttles to max power as the Captain joined him and they both applied emergency power. Within 8 seconds of the right engine rolling back to just above flight idle the left engine did the exact same thing. The engines never changed RPM from that point till ground contact. The F/O continued flying and kept nibbling on the stick shaker to clear a hill just prior to the impact point. Apparently the crew is being hailed as heroes for their performance. The two areas under investigation are fuel that was uplifted in China. Ice in the fuel is a consideration and they are running chemical test at this time. The other area is engine software. So far they can confirm that everything from the throttles to the ECC's worked as it should. Its the info from the ECC's to the fuel controller that is in question. This aircraft had just had a software update 2 days earlier
Jan 25, 2008
By Guy Norris/Aviation Daily
U.K. Air Accidents Investigation Branch inspectors are examining the fuel system of the British Airways Boeing 777-200ER which crash-landed at London Heathrow Airport last week after updating its preliminary findings to say that both engines did briefly produce some thrust during the approach.
The AAIB, which initially indicated that the 777's Rolls-Royce Trent 895 engines failed to respond to an auto-throttle command, now says both engines spooled up when commanded but that the thrust levels soon reduced. The number two (right) engine reduced after about three seconds, while the number one engine power reduced after about eight seconds. The findings appear to be consistent with post-crash photographs that indicate considerably more fan damage to the number one engine than the number two engine, which appears relatively intact. The fan damage indicates the number one engine was running at some power on impact.
Investigators say that "all possible scenarios that could explain the thrust reduction and continued lack of response to throttle-lever inputs are being examined," and adds that flight data recorder information indicates normal performance from both engine control commands and the auto-throttle.
According to the British Airways 777 technical manual the autothrottle is controlled by the thrust management function, which operates the autothrottle in response to flight crew mode control panel inputs or to automatic flight management computer (FMC) commands. Thrust management calculates reference thrust limits and thrust settings, or follows FMC thrust settings as well as commands the thrust levers themselves. The system is also designed to sense and transmit autothrottle failures and commands thrust equalization through the engine electronic controls. The thrust levers can also, of course, be set manually by the crew.
Sources close to the investigation also tell The DAILY that British Airways engineers have been collecting fuel samples from every flight emanating from China. The sample collection, plus comments from the AAIB indicating the aircraft had "adequate" fuel remaining on board at the time of the crash, is believed to point toward suspicions of a heavier-than-fuel contaminant being present. Theories propounded by crew include the possible presence of water in the tanks that, having become frozen during the intense cold-soak period of the flight, partially melted and formed a slush that could have partially blocked the fuel lines.
Sources also tell The DAILY that upper air temperatures over Russia and northern Europe were extremely cold on the day of the accident. Information from other crews coming from Asia on Jan. 17 encountered extremely low temperatures in the -70 to -75 degrees C. range, resulting in fuel temperatures dipping into the -40s. European upper air temperatures also indicate the last 6.5 hours of the inbound China flight would have been flown at an outside air temperature of -60 deg. C. or lower. Although this would have resulted in fuel temperatures on approach in the -35 degrees C range, this would not normally constitute a problem unless, potentially, contaminants were present.
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