What does mean “The FO took control for the landing at a height of approximately 780 ft” did he just come back from a pee … or the CPT fell incapacitate … ?
No. BA fly monitored approaches, and this would be entirely normal.
I still find it odd that the automatics would be left in until the aircraft seemingly stalled. 108 kts in a 777, albeit a fairly light one, must be at or very close to the stall speed. The report states:
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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
As for the crossfeed valve,
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The fuel crossfeed valves indicated that they were closed and they had not been operated during the flight.
This is quite unequivocal and is from the first page of the special bulletin.
After the aircraft crossed the Ural mountain range in Russia it climbed further to FL380 where the ambient temperature dropped to as low as minus 76°C
What is the enviornmental envelope re min temps for the 777. I know the airbus 320 is -70c
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Does anyone know the answer to this question?
No, but it's not the minus 70 that the single aisle airbus's are limited to. After flying the airbus it was something I looked for and it isn't in any of the manuals (BA) so the 777 can be flown in colder air.
Some posters here have mentioned at what temp the low fuel temp warning would activate. On BA 777's the fuel freeze temp can be changed in the FMC but is set to -40 by default, the actual warning starts at 3 degrees above that value. So by default (but it can be changed) he low fuel temp warningwould sound at minus 37.
Offending plastic blank was traced back to manufacturer....
Just as an aside, the debris found in various locations in the fuel system:
- a red plastic sealant scraper
- a piece of black plastic tape
- a piece of brown paper
- a piece of yellow plastic.
- a small piece of fabric or paper
- a small circular disc
Surely this can't be normal. Was it all likely introduced during manufacture, or at later stages during maintenance or refueling?
I don't think you'd describe the debris as particularly abnormal. Fuel tanks often have bits of FOD floating around in them. Try to visualise a 6mm diameter plastic disk and think if you are going to be able to spot that in a large, dark fuel tank.
What this seems to be pointing towards is the only situation in which both engines could possibly have suffered the same fate - an as-yet undiscovered maintenance error either at Cardiff, London or Beijing; or more unlikely, a manufacturing defect.
As so much has been ruled out so far, it is even more likely that it is a seemingly minor circumstance that could have caused such an event. What that event is, however, clearly remains a mystery...
"Eliminate all other factors, and the one which remains must be the truth." - Sherlock Holmes
The AAIB seems to have pretty much eliminated mechanical and/or electrical failures within the engine systems as likely causes of this accident. They are not even suggesting that the cavitation damage within the fuel pump ocurred immediately prior to the crash - it might have happened weeks before the accident. The evidence points to some fuel related factor as it seems to be the only thing common to both engines. Perhaps, there is some aspect of fuel behaviour, under certain conditions, which has not been encountered before and is not yet understood. Cue the fuel chemists!
People should note that the problem SEEMED to affect both engines to a similar extent, but at slightly different times.
The latest report states that they have tested the fuel and it conforms to the required specification.
The debris was different in each wing tank and somehow would have had to have the same effect within 7 seconds on each engine (!)
The fuel metering valves were stated to have moved to the correct fully opened position and the filters filters were clean, as for the Fuel Oil Heat Exchangers one was clear and one had slight debris - the high pressure filters were clear.
It SEEMS very unlikely that the fuel was to blame, and the debris could not cause the same effect on the different engines.
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I cannot see that two separate pumps with whatever minor damage could possibly both fail within 7 seconds of each other (whether or not they subsequently showed no fault).
I have no idea about what caused the problem, but would like to know more about any flowmeters that are in the system. Also about what could cause fuel aeration.
However, it gets annoying when people don't think about what the report says before posting. Anything that occurs must be able to affect both engines within a very small timescale.
The cavitation damage to the engines' HP fuel pumps would seem to indicate incipient fuel starvation - or at least aeration - for whatever reason. Cavitation damage occurs when the pumps lose their continuing lubrication by the fuel itself. None of the in-tank debris (plastic etc) found would explain one or (particularly not) both engines becoming fuel-starved.
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The possibilities remain prima facie limited to establishing the reasons why fuel (or trapped water) could be cooled to below freezing point (even if that point is 10 degrees below the specification freezing point for JET A1 of minus 47 deg C). The pointer would seem to be towards either water in the fuel becoming frozen or waxy/illiquid. There's another possibility however.
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Think about the fact that certain "aerodynamically quiet" areas on an airframe can accumulate de-icing fluids and cause flight-control restrictions (see instances by Googling that term ["aerodynamically quiet"] and recent and historical AD's - particularly for BAe146 etc). In a similar fashion, icing will not form and accumulate uniformly over an airframe. It will first be seen in the corners of windshields, along windscreen wipers, wing/tail leading edges etc. Now think about what can happen in another fluid (i.e. not air, but fuel) that's contaminated with very cold water. What I'm getting at here is that some quiet (or stagnant) areas in an LP fuel system (tanks thru to HP pumps and filters) can support the formation of ice or waxy deposits due to higher (than normal/ambient) super-cooling in certain discrete areas. Result could be (a) large(ish) lump(s) of melting ice that will find its (their) way into a critical passage, filter, pipe or valve and temporarily cause constricted flow-rates. Because both sides of the aircraft mirror image each other, it's conceivable that identical "releases" of this icy lodgment could occur almost simultaneously - and then disappear (i.e. great quantities of water would not be required and wouldn't later be detectable anyway).
However why limit oneself to considering frozen water? Why not just think in terms of fuel itself being trapped and frozen in fluidically quiet areas and becoming supercooled/frozen. I'm guessing that residual fuel in the center tank/tail tank (and their collector tanks) might qualify and could later be induced into the system by both warming and the attitude changes inherent in both descent and configuring (gear and flap extension).
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At what temp would the low fuel temp warning activate? On BA 777's the fuel freeze temp can be changed in the FMC but is set to -40 by default, the actual warning starts at 3 degrees above that value. So by default (but it can be changed) the low fuel temp warning would sound at minus 37.
However, as with all such system measurements, the validity and usefulness of the sensor data depends upon where the sensor is mounted. Temperature measurement systems are inherently different to pressure measurement. Pressure is exerted equally in all directions. Temperature can vary over a significant range within a large volumetric system, some of whose components/areas are temporarily isolated by dint of being virtually (but not really) empty. If a center tank's output to the wings ceases relatively early in the cruise attitude (because it's "virtually" empty), does that mean it cannot thereafter contribute some previously "baffled" slushy ice-dregs (merely by gravity feed perhaps) once the nose lowers to the descent attitude? It's also a liquid fact that smaller stagnant quantities (such as dregs) will freeze sooner (and also melt sooner) than larger quantities (i.e. in wing tanks) that are being subjected to throughput recirculation (of bypass fuel), engine feed and fuel/oil heat exchanging etc. Wing carried fuel is also heated to some extent by the wing's passage through the air (and by the sun on the upsun side). That's not the case with fuel carried (or baffle-lodged) in the center-section and tail-tanks.
Why would this have happened to BA038 and not other 777's previously? My guess is that there is a trigger temperature and that the period that G-YMMM spent in the super cold pool of their track-miles between the Urals and Eastern Scandinavia ("unusually cold but not exceptional" - UK Met Office) may have allowed such pockets of super-cooled fuel to form into ice. The time of day (sun/no sun) and chosen CRZ hts may have also helped format the process.
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This is probably nothing, but since lots of posts are equating a loss of upstream fuel pressure (upstream of the HP fuel pumps in the engine) with a blockage in the fuel line (causing cavitation), it's as well to realise that it's not just a blockage that can result in low fuel pressure from the LP pumps (in the wing tanks).
A few years ago we were completing maintenance on a Fokker 100 and for some reason the LP fuel pump delivery pressure on the pumps in the LH wing were only delivering about 50% of what they should. To troubleshoot, the pumps on the LHS & RHS were swapped - the problem STILL only occurred on the LHS. That eliminated pumps as the problem, and we started to look for a blockage in the lines downstream of the pump as the only explanation. No joy.
During the maintenance input, the LH engine had been changed. This required swapping the IDG (integrated drive generator) from the old to the new engine. During that procedure, human error had misconnected the three phase wiring and earth so that the AC three phase output from the LH engine generator was wrong.
Lesson No 1 - no other system on the aircraft was bothered by this except the LH fuel pumps. Lesson No 2, although the Ground Power Generator Control Units monitor the phase quality of the power coming to the aircraft, ordinary Generator Control Units do not (on that aircraft anyway). So there was no fault announced at the front of the aircraft.
Now in no way am I suggesting that on this 777 the generators magically re-connected themselves in flight. However sudden low pressure from all LH & RH pumps could (in theory) occur if the phase relationship of the power supply to all of the pumps suddenly changed.
Also, if the 777 is anything like the Fokker 100, it might only be the fuel pumps that would have a problem with this. How that might happen in practice I don't know - I would think it so unlikely as to be almost impossible. Also, even if it did happen, I would be surprised if such a loss of pressure starved the engines - but perhaps in combination with other things it is (theoretically) possible.
One centre tank water scavenge jet pump suffers poor flow due to 6 mm disc
Frozen water accumulates to be discharged at late stage of centre tank scavenge.
Hard ice crystals abrade fuel pump surfaces
Can frothing occur also?
One of the crossfeed valves neither fully open nor closed after crash,(and according to Captain MM would not have been selected open in any case(?))
The enquirys lack of comment indicates it to be serviceable,
But if it had in fact for some reason remained half open throughout the flight it would supply the missing common factor complete with 7 second interval
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.
Would cavitation not have to build up over a period of time in order to be described as 'abnormal'? I appreciate that if solids peppered the bearings and ports then there would be increased pitting, but to such an extent in one flight leg?
What pressure (psi/bar) is the fuel entering/leaving this device?
Today, 01:09 #97Wornout Rubber
Instead of being 'just another number' I could order a Personal Title and be a bit different
Join Date: Jan 2008
Location: Dubai
Posts: 10
Best Glide Speed
Can anybody comment as to the best lift/drag speed (best glide speed), with Flaps 30 on a B.777?
The AAIB stated that the speed decayed to 108 Kts.
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Anyone have simulator access that can answer the question?
The formula (found on internet...) is TAS x 100/sink rate (FPM) = glide ratio.
IE 250 KTAS x 100/1300' = 19.2
Try a couple of different speeds, and various flap settings (20 being the most interesting due to the reduction in LE slats), and you'll come up with the answer.
Modern airliners are around 18:1. Easy formula is altitude in thousands x 3 = glide distance for a clean aircraft at best L/D speed. Eg, 30,000' x 3 = 90 n.m.
QRH for my a/c has best L/D speeds(clean) listed under "Dual Engine Failure".
Last edited by misd-agin : 19th February 2008 at 16:32.
Reason: spelling
Whatever the best glide speed might be, a reduction in speed can only build induced drag more and more so the overall L/D must diminish. And this will be non-linear - ever diminishing performance as speed decreases.
Perhaps the autopilot is not the crew's best friend in these circumstances.
PS. I thought landing flap was normally 25 degrees, AAIB say 30 was set.
I recently had to replace a propellor on a boat.
The reason? Cavitation damage to the blades!
Considering the prop normally sits fully immersed in water there wasn't a lack of water around it.
In this case, cavitation was caused by the prop rotating so fast it caused a decrease in pressure. This caused water to boil at a lower temperature.
When the bubbles from this boiling burst they can cause pitting to occur on the blades of the prop.
Incidentally this is something to be avioded if you are in a submarime and do not want to be detected on passive sonar!
I believe the cavitation noted by the AAIB was as an "observation" only. The manufacturer has stated they could still deliver fule as specified. To me the reason has to be a restriction in both fuel lines.
It would be interesting to inspect the rest of the B777 fleet for cavitation damage to the pumps.
Could this just be one of those one in a million accidents?
Last edited by Mig15 : 19th February 2008 at 22:19.
Today, 01:09 #
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